Rock Band's controller compatibility was a touch confusing prior to the game's release. Now that it's out...still confusing! Despite earlier reports indicating they would get along like a house on fire, it turns out the wireless Les Paul guitar from PS3 version of Guitar Hero III doesn't work with Rock Band. Anyone hoping to get some guitar and bass action in before the individual instruments are released next year, sorry. No. "But they can fix it in a patch", I hear you whimper, "right?". Right? No.
Harmonix have issued a statement regarding the matter, which reads:
Harmonix develops and bases all of our games, guitars and other peripherals on open standards established by platform manufacturers such as Microsoft and Sony. Rock Band is no exception and supports an open controller standard. Guitar controllers are like any other standard game controllers—the controller sends a signal back to the game depending on the buttons you push. If a third party game controller is based on open standards, then it should work with Rock Band as well. If certain controllers do not work with Rock Band, questions about those controllers should be directed to the peripheral manufacturer. In addition, we welcome any 3rd party software that wishes to support Rock Band guitars. If a 3rd party guitar / music game does not support the Rock Band guitar controller, questions regarding this should be directed to the game manufacturer.
In other words, blame Red Octane, not us. One Guitar for Rock Band [IGN]