Very late reply so you might never see this... but I have a full complement of RB and GH hardware, and a long-term project I'm investigating is ensuring those rhythm games can always be played via Dolphin even once all the 'toy' hardware is dead and buried.

Specifically: I want to add direct support for proper e-drums played via MIDI into Dolphin, without the various hacks to get it to emulate a keyboard etc, and compatible even with the Pro Drums mode in RB3.

Guitars are simultaneously an easier and harder question: would require a DIY guitar, but can be fed into Dolphin just by emulating a HID device.

email is in my bio if you want to discuss