I don't see anything wrong with it. Illogical, and a waste of money perhaps, but that's not your problem. Be thankful they are not demanding inappropriate music selections.
Then again, you never know who's invited the wedding. Perhaps there will be some in attendance who will want to sing along on the propers!
Imagine baritones in the congregation bellowing the soprano line of Mozart's "Ave verum" during Communion and you might understand my concern.
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