I found the rule I was looking for! If anyone else has this question, it's in Tome of Battle (Bo9S) page 43: ". . . you cannot combine special attacks such as sunder and bull rush with strikes. . . ."
The PHB lists trip, disarm, and grapple as special attacks, so that's pretty open and close. I'm still not sure if trip, disarm, and grapple can be treated as melee attacks for all other purposes, but for ToB maneuvers, they are not.