*actually has two of those controllers for the actual drums
The lack of triggers on that Rock Band controller are precisely why I've never tried using it as a shmup controller, since my bombing reflex is attached to having a right trigger. There's an interesting alternative in the foot pedal though. I've never used it for bombing in a shmup, but I've mapped it to Alt-F4 and used it to save my ass in my limited adventures in Diablo 2 Hardcore. As with any other kind of obscure control scheme, it can take some getting used to, but keep in mind that the option exists if you're feeling experimental.