I guess YES, they are a nice addition to that time.
As Akhil Sharma pointed out, those soldiers are dropped at a specific point in time. There is nearly one year preparation time until they have to be ready for the first siege, and another year until the siege really takes place. Yes, our people will be weaklings with weak feet needing toilet paper in the beginning. But they have a year preparation, maybe even more.
We can't quote Romans in any way - they were in some sciences much ahead of middle-aged Europe, even if they were using lots of bronze and leather instead of iron. But that knowledge was not transported far and much of it was forgotten in the pox chaos and church panic and Roman Reich breakdown that the Europeans had to endure.
So let's just assume that the crusaders used standard tactics for their time, trained their weapons to perfection on their three-years-journey from Europe to the middle east, finished the first crusade, and when godefrey is already in his last year, our soldiers drop. And have no clue.
They will be bigger than the average European of the middle ages, roughly the size of well-nourished nobility people. Language is handwaved, so they might be able to convince somebody that their leader is some low ranked third born nobility guy, and thus being able to get an open ear in the leading ranks. This is the first difficulty someone from today will encounter - normal people were not listened to at all. Hopefully they have a captain or lieutenant who is good with words.
There, this guy, if he is good, can place some interesting messages. He can spread the knowledge of flag signaling, morse coding, Napoleon's concept of small hide-able movable units instead of big size armies, WW2 concept of the operational layer between tactic and strategy, sand filters for water, boiling of medical equipment, tactics that knights are not only run fast to the flank of a battle or support a weak spot (which has been done as standard) but maybe they can think of some tactics that allow knights to appear in several battles in short succession.
This is all the communication, logistic, operation, hygiene stuff that has been said before in this thread.
But now, if this counts as not-allowed transfer of technology to former armies, there is still much good they can do. There are 50 years until the second crusade, and those people are not needed in the coming three sieges, and they know it!
So, that's a strategic time scale, not a tactic time scale. We don't drop them into the middle of a sword fight, that'll be stupid. We could (they have one year time to train!) but we can make better use of them.
Multiplication: founding of families and uprising of children in the name of the crusader culture until the second crusade comes. Each second surviving child can be an additional soldier for the battles to come. If the soldiers of our unit teach their family sand-filtering of water, basic (mouth)-hygiene, reading and writing, we'll have an army of healthy individuals.
One of the reasons the crusades were failing was because culture eats strategy for breakfast. The crusaders had some military successes in the beginning but were then failing to root their culture into the people. So they needed continuing support from the homeland with an easy-to-disrupt 3000 km support chain. Imagine they had proper support at the front in the middle east, they could have done far better. If we plant 300 dedicated men in that culture and let each make 5-10 kids as was normal in these times, that's a lot of push on the cultural front.
Canalisation/Water filtering and Garbage disposal: If those 300 families would push for both of these facilities in "their" city(ies) or village(s), they would be hardened against smallpox and cholera. Pox were depending on rats living in the garbage; cholera results from drinking water with microbes from other sick people. So it may be that just from these basic measures, they get a population which can "deliver" much more soldiers to the second crusade 50 years later, even when we cannot bring antibiotics.
Again Canalisation, this time for the watering of plants. Along with the digging of wells, that's one of the biggies. You want more soldiers, you need to feed the people! Everyone who dies of hunger is one swordswinger less. Everyone who is fed by their new masters is a potential friend and not an enemy.
Again, Garbage Disposal. Fertilize the crops! Don't know if it was known, but it certainly is a biggie if this wasn't done before.
It's roughly known from where Sarazin's soldiers were coming. So what we do positively to the crusader villages, we do negatively to the opposing villages. If we constantly poison water supplies, (re)-introduce pox and cholera, steal and burn crops, interrupt or kill caravans, again and again all few years, over the course of 50 years this can severely shrink the numbers Sarazin will bring. He had maybe of 100 000 Soldiers when he ended the crusades. No tactic will ever be good enough to go against this, also not with 100 or 300 extra soldiers from the future. But 50 years are a long time.
If that's too evil, send priests. Culture eats Strategy for breakfast. Convert people to Christians or at least convert them to people opposed to the ruling caste, build a network, when the day comes, have people inside the wall who attack the door.
Ok, you don't want all that?
If introducing modern organization and tactics is not a forbidden technology, you could do just that.
Ancient armies used to stick together because it was wise to do so. Side effects are, to build up a camp site and to start again the next day was wasting hours. I can imagine that the first soldiers were arriving at the new campsite when the last soldiers were just starting their journey the same day. So there is some kind of "Soldierworm" in the landscape that is easy to see. The "Worm" is surrounded by scouts - they have horses, they are freed from the camp work, so they have additional valuable hours and speed to check the area. They will report in what they see, and if they don't report back, that's a message, too. The General might then send a small horse-unit that way to see if he can get the evildoers.
And here we have a use for our modern small-unit hide-and-seek tactics. Harass those scouts, maybe even fight the knights that come after them, then disappear as good as possible. Do that from all sides. I don't know how much damage they can do that way, but as they'd never fight 1-1 I guess they can do some things.
There is also a worm of civilian cars following the army, with food and water and smiths and prostitutes and everything a soldier might want to spend his money on. If those are attackable, it might be a juicy target indeed.
Finally, armies were used to not having any logistics. They were feeding of the villages on their way; often they were as bad for friendly villages as they were for enemy villages, just because they were using all the winter stock for themselves. I've read the Simplicissimus, a story written during the 30-years-war which was 500 years later 1618-1648. They STILL had no proper food logistic then. So I guess in the crusade, they also had those small units of soldiers with the task to "empty" the surrounding villages (friend or foe) to feed the army.
Attacking those might be efficient indeed. No General would send his entire army for food, those units are small, 10-50 people. And here we go. Kill one of those units, get away, kill the next, get away.
Getting away is the difficult part. You leave traces in those times. Rare is a road made of stone.