Are music reality show questions on-topic?
Good question. Their status on Movies & TV seems a bit vague, and it's unclear if they're a good fit there.
Personally, I think that questions regarding music or musicians should be on topic here even if the music or musician in question perform as part of a reality TV show, but questions about the show (its production, hosts and so on) shouldn't be.
I think - as always - "it depends"
Who do you think will win this year's X Factor?
is as far off-topic as it can get.
Don't you think so&so was out of tune on Sunday?
However, Leona Lewis/JLS et al have far outgrown their reality show beginnings & would be a valid topic of conversation (whether I like them or not;)