You got me on that one. I'm not finding anything prohibiting it, but it sure seems like something about allowing other faiths to use the building would be addressed somewhere.
Closest I can come is Handbook 2:
21.3.7, "Other Faiths".
A few things I did find: The handbook says the wedding is to be simple. A wedding march is not appropriate. No video or pictures if done in the chapel. (Handbook 1: 3.5.3).
(Prohibited): "Hosting speakers or instructors who are paid a fee" (Handbook 2: 21.2, Item #5)
Some of these restrictions could settle the issue.
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