"PS3 Controller Compatibility Routine Patch
Good news, see below (this patch should be available quite soon, maybe even up now as of this posting)-
Available today is a routine update for the PLAYSTATION 3 version of Rock Band that addresses a number of items related to guitar controller compatibility. Should Rock Band owners choose to obtain the update, they will need broadband internet access connected to their PLAYSTATION 3. The update will be downloaded once the game is started.
The patch will be available today but is not yet up for download. Keep watchuing your Rock Band.
[Via Rock Band Forums]