Not at all. You can do what ever you want in the studio, but when it comes to live music, there should be nothing pre-recorded. Electronic performers playing along with obvious loops are one thing, but you shouldn't be sneaking in any enhancements. Behind a curtain??!!!?? C'mon now! (Oh, but i wouldn't mind being the director of a ten-piece funk band.) This is from the free Keyboard magazine i got sent in the mail, so no link:

Hey Mike, I enjoy reading your articles very much. Among other things, I'm the musical director for a ten-piece funk band. We've experimented with backing tracks with mixed results. I see you're on the EWF Live album from '96, and I was curious if there was programming on that tour. You guys seemed so tight I would be a little disappointed if it was pre-recorded. However, I'd love to know to what extent it was. -David.

David,
I was with Earth, Wind & Fire from 1987 through 1997 or so, at first playing keys behind a curtain and doing keyboard tech duties. Then in 1993 they put me on stage. When I first joined them, I was using a Roland MC500, later an Atari computer (1040ST), then finally a Mac IIci using Performer. There were not a whole lot of extra parts being played from the computer on those shows. What was there was mainly enhancement. If the computer died, the show would definitely still go on.
Typically on a song like "Let's Groove" we'd double the bass part with a synth bass, put the 747 jet sound and other effects in the computer, have some percussion loops from the original recording, and double the background singers. On songs like "Reasons", the computer would drop out after the second chorus, and we'd be off the click from there on. We never used any lead vocal tracks, just backgrounds. So, to answer your question, the show was definitely not pre-recorded. The key to making extra tracks really work is having a great drummer like Sonny Emory that can play well with a click.
Honestly, there are only a few bands out there that don't do this to some extent, but nowadays there are defintely not as many bands just playing back everything like there were a few years ago.
Thanks for the kind words!
-Mike