Every animal humans want to domesticate must conform to a series of criteria. This is why we didn't domesticate rhinos instead of cattle, or lions instead of dogs.
To be domesticated, an animal must:
- Have a varied diet and thus be willing to eat humans' scraps
- Grow fast - the longer an animal takes to mature, the longer it takes to make it valuable
- Be willing to breed in enclosed spaces in captivity
- Be "pleasant". Yes, some domesticated animals like bison are aggressive, but we have to keep them in massive enclosures.
- Be calm and "brave". An animal that runs away every time you step towards it cannot be domesticated.
- They must have a flexible social hierarchy
So, to determine whether Entelodonts are a viable candidate for domestication, we must see if they comply with these points. Obviously, we don't know some things about them, so we should leave room for educated speculation.
For the first point, entelodonts are fine, since they are omnivores. Omnivores also tend to be opportunistic, so would eat food given to them by humans if they thought they were safe.
I've done some light research on all known Enteledont genera, but could not find out when they reached maturity. In this case, I will have to look to their modern relatives. Pigs reach maturity at 6 months, but growth rate will be different for carnivorous animals. The entelodont Archaeotherium was a predator that is thought to have cached kills, indicating a similar niche to the leopard. Carnivorous animals are usually more intelligent and "skilled" and therefor take more resources and time to raise. The leopard's maturity rate is considerably higher than the pig's, at 2 years. I think that's an alright amount of time, and anyway it will decrease after selective breeding.
Both hogs and modern terrestrial apex predators seem to be okay with breeding in captivity, so I will assume there's a yes to the third one as well.
This is where it gets tricky. I'm not sure if an entelodont would "be pleasant" with humans. But, if humans can domesticate wolves and half-domesticate bison, I wouldn't put it that far past them to do it to entelodonts.
There is little documentation I could find on entelodont behaviour, but I'm gonna go out on a limb here and say that "They probably weren't skittish". Far larger than humans, with bigger teeth, I somehow doubt they would have much fear of us once they became accustomed to our presence.
I think that the last criterion is good with entelodonts too. All evidence indicates that they weren't highly social, such as scavenging, caching prey, omnivory etc.
Therefore, I think that entelodonts could potentially be domesticated. Domestication is a bit of a gamble, and it is never a guarantee that it will turn out right. But if we did domesticate entelodonts, what would happen?
The general rule is that domestication makes the species smaller and dumber. They don't need to find food, survive predators and other dangers, or really do anything except eat, sleep and breed. All that doesn't require much processing power to do, and bigger brains cost calories, too.
If you are domesticating the entelodonts for transportation, they will grow stronger. If you domesticate them for war, they will become more aggressive and less responsive to things that would normally distress them, like the death and loud noises of a battlefield. If you want them for aesthetic purposes, they will become more extravagant, or their hair will change colour, or their tusks will grow longer or whatever you want.
So, to summarise:
Entelodonts could be domesticated, and they would change overtime depending on what you're breeding them for