Yeah, you can (in theory) have as many devices as you want on the same MIDI channel. Just be careful with the lengths of your MIDI chains though - you don't want more than 4 devices in series or you can have timing issues and data corruption. If you're running more than 3 or 4 devices, it's well worth getting a MIDI thru box (splitter). MIDISolutions make an excellent one for not too much money.