So, since I was moving to PS3 and all, I didn't want to rebuy all of my equipment. (1 RB2 guitar, 1 RB3 Pro Guitar, 1 MIDI adapter, 1 GH5 drumset, 1 GH5 guitar, 2 mics, and 1 RB2 Drumset all for Wii.) So, I knew the mics would work already, one of them was my cousin's who owns a PS3, and they're USB mics that would work either way.
So, my stupidity mode turned on, which later turned into sort of clever. I plugged my Drumset and Dongle in to the PS3, and the PS3 actually RECOGNIZED them! So, I got my borrowed copy of Rock Band 2 (also my cousin's), inserted it into the PS3, and ran into the problem.
THE PROBLEM WITH IT:
The PS3 thinks they are normal controllers, so you'd really be playing vocals.
I'm trying to find ways, but just searching "How to get Wii Guitar and Drums to work with PS3" would get me answers like: "No, are you stupid? Wii instruments go to Wii, and PS3 instruments go to PS3! Shut up you ******. Jeez, are you stupid?" So, I searched if there was any problem getting a normal PS3 Guitar to recognize as a guitar and not a normal controller. I did this because I wanted to see if there was any way of assigning a controller to a name or whatever that would make RB2 work with the controllers.
I have not found anything, yet, but I'll keep looking. I'm the kind of guy who ignores "Reinstall" or "Send back to the store" or "Restore" or "Get a different one." I don't give up on stuff that could help other people. Even if there is no way, at least I found out the PS3 actually recognizes these instruments. And I know why, it's the same reason they are recognized on your PC. They're USB controllers. Game controllers.
It's also interesting because it recognizes "A" as "X", and every other button as a matching button. Heck, the button you press to connect the guitar or drumset to the Wii works as a button to the XMB menu on the PS3
Now, I know I'm using RB2, but this might also apply to Rock Band 3. (Unless HMX already knows, and fixed it, but I doubt that.)
I just wanted to share this story, because most people don't even try, and I have made it this far with compatibility.