Oh dear. According to this Joystiq story, the PS3 version of Rock Band 2 doesn’t recognise Guitar Hero: World Tour’s drum set.
This may sound trifling. In fact, it is. Unfortunately, SCEA specifically promised instruments from the bigger rhythm action games would work with each other this year, citing the two titles as an actual example.
“A few specific examples include: Guitar Hero: World Tour’s guitars and drums will work with Rock Band 2 and Konami’s Rock Revolution software,” said SCEA’s Michael Shorrock in August, at the time of the feature’s announcement.
Harmonix is looking into it, apparently. As you do.
Watch for someone to confirm it does or doesn’t work with the 360 versions: Microsoft promised the same thing.