guitar hero rock band  

Yes they can. I know the guitar hero drums are different than the RB drums so idk how you really play but it DOES work. I prefer the GH guitars and the RB drum set. keep in mind you CAN use the GH stuff with RB but NOT vice versa. It only workes one way. Some wierd liscencing stuff or somethin. lol

Yes you can use guitar and drum in guitar hero for rock band.

For guitar, the fret buttons are basically the same color and positions. The only difference is the note in guitar hero is round while the ones in rock band are bars.
For drums, the guitar hero drumset has more drum buttons than rockband so you'd just have to ignore one. The rockband has only four and one for stepping so you can't use it for guitar hero.