But imagine a post-grunge/metal Pokemon band. For example, a Trainer can have vocals/guitar, one Pokemon can do bass, another can do drums, that kind. Also, said Pokemon could use their voices as a way to accentuate the Trainer's own voice. The band I had in mind was a Pokemon-ized version of Three Days Grace, whom I simply can't think of a name for now.
Lead Vocals/lead guitarist (Human)
Bassist and second voice: Raichu (Explained a bit later)
Back up: Either a Ditto or a second human.
Raichu appears to not have any fingers, so the idea is for it to strum the notes (With it's tail, for instance) while sending an electric pulse through the base, causing the desired sound. Raichu (Especially that of Lt. Surge) appears to have a rather gravelly voice, so it works as a secondary voice to reverberate.
I was really bored thinking this up, and I was listening to a Three Days Grace song, so...yeah. This will never be implimented in the anime, simply because of Japan's influence, but I can easily see a similar sort of concept.