In OR/AS, there were a few Horde Trainer battles with Aqua/Magma grunts. It's pretty much exactly the same as wild horde encounters, but with five trainer's Pokemon instead of five wild Pokemon. I believe there was only two of these types of battles in the entire game.
What did you think of this concept, though? I think five vs 1 trainer is really unfair, but that's evil teams for you, right? At least the game balanced it in a way by making the five Pokemon all extremely low leveled.