Excerpt: Situations that require caution are those that involve mixing Xanthichthys with small, shy or passively feeding fish. Although the triggerfish will not likely physically attack them, the smaller fish may feel threatened and thus hide constantly and/or fail to feed. This is certainly not an ideal situation and is best avoided with a little forethought about the adult size of all fish concerned.
I keep a blue throat trigger with 2 false percs. The clowns seem to hold their own against the trigger however I can tell that they are apprehensive when the trigger comes near them. The good thing about adding a trigger is that no other fish will mess with it.
This is of course my experience.
btw - I also keep clams with the trigger.