I know that some of the programs available for pre-recorded music now allow for tempo adjustments. I remember seeing a production of THE BOYS FROM SYRACUSE in which the prerecorded orchestra was fantastic, but every time a song began the pace of the show went to hell because the tempos were too slow for the comedy.
TOD
I remember seeing a community JESUS CHRIST SUPERSTAR performed to a CD that someone had created, that at the time I thought sounded pretty good, and pacing/spontaneity didn't seem to be compromised.
My only other exposure to tracks would be a larger production of BEAUTY AND THE BEAST in which the MD used MTI's OrchExtra or whatever it's called, and that is completely controllable. It was pretty damned impressive. Or it seemed so, since I'd never seen and heard it used before. He "played" that (it's done on a tiny keyboard) and conducted, and had a live drummer and bass player. But you heard a "full orchestra". And like I said, all the tempos, etc., are totally in his control.
I know I've heard a couple of professional productions sweetened with the use of that (or something like it), but those don't count because there were a fair number of live players.