I have a three-stripe and two true percs. The three-stripe has a rock, which incidentally is the rock he hitch-hiked home in, and it is HIS ROCK. But he doesn't pick on the clowns at all--in fact, I see the bigger clown dive at him from time to time during feedings.
I think it's really hard to predict "yes these fish will get along" or "no they will fight all of the time." Read and learn about your species, ask the advice of friendly hobbyists, but you will always have to be ready to step in and take action if necessary, IMO. You can see just by reading this thread that no two fish are exactly alike.