Are/were there non-Mormon faculty and staff at BYU? Do/did they have to pay the tithe?
Yes, there is/are (at least one non-Mormon...perhaps a few)
There's a woman with a Christian background who is the advisor to the Christian group on campus. [BYU allows a certain % of non-Mormons to attend; many of whom are of a Christian background]
Do they have to pay the tithe? (No)