So I've done a bit of reading, and from what I gather, it looks like GHWT drums on RB2 work for 360 only now, and not PS3. Also, it's just a 1-1 mapping - it just doesn't use the orange cymbal. RB2 drums in GHWT get re-mapped to 4 pads. Also, activating star power with the RB drumset is a bit wonky, as it requires hitting the red and yellow pads at the same time.
There are quite a few problems people are reporting with the drums, and Activision has a lame return policy which has you pay return shipping costs (and no send-first option).
Seems there's an expected split between which game has the better mapping.
Here is an awesome post with links to youtube comparisons of each. GHWT does the GH-standard 3-button chord overkill, and RB is a bit more simplistic (realistic?).
Here is a good review and discussion of the GHWT drumset.
So, looks like I'm skipping over GHWT altogether - both the game and the instruments.
The guitar is supposed to be nice, but I have 2, and really have no problems with either. I love the RB guitar, and the GH2 X-plorer still works perfectly fine.