My dergs: About the size of a large draft horse, 12-meter wingspan, human intelligence, able to talk in human languages.
Scales are very tough, but an armor-piercing round from an M2 Springfield bolt-action rifle can rip through, even if with greatly diminished energy. The dragon would certainly feel it. As always, the 50 BMG makes dragons tremble with fear, well, until a dragon shows up with a smart grenade launcher, as arc-over, proximity-fuse 'nades go BLAT! BLAT!
Dragons can carry the weight of a human on their backs and have steady cruise speeds of 35 m/s. They require the same ground clearance as a quetzalcoatlus when taking off.
As for stealth, we went over several options, I'm going with a natural radar-absorbent coat for my dragons. Well, they supposed to be capable of producing CNTs and the multi-walled ones can be radar-absorbent.
Even though they're the toughest biological flying creatures in my setting, dragons can't hold a candle to gunships or helicopters.
However, helicopters can't soar (even an autorotating helicopter will still make noise) and gunships have trouble landing on rough terrain.
It's clear that dragons won't be actively fighting on the frontlines, and why should they? It's rather chaotic and way too dangerous, whereas you can make scouting pretty adventurous too, and just as important.
However, I'm not sure what type of recon should they be doing? Could they be a part of a semi-early warning radar system? Would they search for interesting things that are on the ground or in the sky?
Assuming these scout dragons are part of a modern army, what type of recon would they be doing routinely?
And before you ask, I mean recon as in military reconnaissance mission. No, Fafnir, it's unlikely you'll find enemy hideouts in the bar, at least not in your current mental state.
Also, dragons are supposed to be able to crawl like a leopard. Sure, they won't go as low as leopards, but still better than nothing.