Yes, I played Guitar Hero Metallica with the Rock Band mic and it worked great.
no
guitar hero, yes, band hero, sometimes.
All Guitar Hero Instrument are compatible with Band Hero.
no, you need to buy either Band Hero or Guitar Hero World Tour's complete band set to get the microphone
Yes, but only from Rock Band 2 and up microphones. After a while Guitar Hero and Rock Band made their controllers compatible with each other (around the time The Beatles Rock Band/Rock Band 2 and Guitar Hero World Tour came out) which means any controllers from those games and higher are compatible
Assuming you are asking if different instruments from GH/RB are compatible with each other in Co-op/Band play, then yes.
Yes it is compatible \X...X/
Yes
Yes. The Guitar is compatible with both guitar hero 2 and 3. Also, the guitar hero guitar on xbox 360 is compatible with rock band for xbox 360.
The Guitar Hero 3 guitar is not compatible with Rock Band on the Wii. And the Rock Band guitar is not compatible with Guitar Hero 3. You can try anyways but I'm pretty sure they don't work.
Yes you can either get the Band Package: Guitar Hero Game, Drums, Guitar and Microphone or the single package only consisting of the Game and Guitar
Yes the guitar hero guitars are completely compatible with rock band.