Wired is reporting that at E3, Guitar Hero director Brian Bright confirmed that Rock Band (the original one) instruments would not only work fine with Guitar Hero: World Tour, but that you could use any electronic drum set with the game as it will ship with a MIDI connection on the back of the drum kit.
This also allows for the addition of another bass pedal if you want to play dual-bass drums. This news flying in the face of Rock Band 2¢s almost unchanged drum setup that will allow for 2 cymbals to be added for another $30 or 40 fee for the accessories post-purchase.