After playing in many West End and UK tours as well as then working at a theatre for 5 years seeing all the toring shows come in i can say in the UK (And Broadway) its pretty standard practice.
We had a click track in Fame for 3 songs (Dancing On The Sidewalk, Hard Work and Fame)
Shows which came to the Palace Theatre Manchester where i worked nearly always did. We used to hear them testing the click tracks prior to letting the audience in
The worst offenders were
The Wedding Singer (over 8 songs for the ensemble were pre recorded)
Singing in the Rain
We Will Rock You (nearly every song with Ensemble in)
Mary Poppins (Steppin Time and Anything can Happen)
Mamma Mia (Most of the ensemble numbers)
Miss Saigon (About 4 songs)
Footloose (ensemble bits on Holdin out for a Hero, Lets Here it For the Boy, Im Free and Footloose)
Flashdance - (4 songs)
And thats just a few
former sadm2 (wink)