Instrument compatibility between all these games is quite fickle, especially on the Wii.
Go here for the compatibility matrices, last updated Dec.10, 2008: http://www.joystiq.com/Instrument-Compatibility-Matrix/
Do take a look at the various notes cited at the bottom (for any cell that has a yes or no answer with a number beside it).
Also there is a 3rd party guitar that is about to be released that is supposed to work with all versions of both GH and RB. You can read about it here: http://nintendo.joystiq.com/2009/02/...uitar-hero-me/