Great Question!
I actually demonstrated this working at an Apple Pro Studio Tour in Manhatthan in October after Logic 9.1 was released for something like 1600 Logic users : )
I actually had 2 Novation Controllers (a ReMote SL and a Nocturne) a Euphonix MC Mix and a Native Instruments Maschine all plugged into Logic simultaneously running on my Mac Book Pro. Everything seemed to run just fine : )