It sounds like you will be fine, Riv. No one is likely to inspect your shoes that closely. (had a quick visual of a maitre d' on his hands and knees checking out the appropriateness of your shoes.
) And, I have seen many men of the cloth in clericals on cruises. Just be prepared for those who assume you are on "duty", not on vacation. HAL does actually hire religious leaders at times. On one HAL cruise, the 14 days covered the entire week of Hanukkah, and they had a fabulous Orthodox rabbi on board plus a Catholic priest and protestant minister, since it was very close to Christmas. Some great conversation ensued, but I got to know the rabbi and his wife on a tour and they were rarely able to just relax and enjoy themselves.
Your wife's idea sounds fabulous for a formal night. You will undoubtedly look stunning together.