Is it the uber pushy dominant dogs that piss him off, or actual alpha males? My Greyhound does NOT accept any other dog throwing their head over his shoulders or humping him. To me those behaviors are not behaviors of an alpha, they are the behaviors of a pushy wanna be. An actual dominant alpha dog rules quietly and calmly. My two never feel the need to mount or throw their heads over anyone's shoulders, or chest bump, or any of that. They walk into a room and simply by the way they hold themselves everyone knows who's boss.
My Greyhound (and probably my pit mix, but he'll never be given the opportunity) will "go off" on any dog who tries to do that. But his "going off" is correcting. I am fully confident that he isn't being aggressive, he's just teaching the other dog manners. Now I don't know your dog. He could be just correcting the other dog, like mine, or he could be getting ready to go. With pit bulls I would never give them the opportunity to correct like that because corrections (and play) can get heated and can turn into fighting very quickly.
My advice is just to keep him away from dogs who are pushy like that, it's the safest way to go with pit bulls IMHO.
"All changes, even the most longed for, have their melancholy; for what we leave behind us is a part of ourselves; we must die to one life before we can enter another." -Anatole France