With his love of Tulane, I recommend that your son apply there as Single Choice Early Action. Tulane loves students who love it, and is very averse to being considered a safety (not that it would be for him).
http://admission.tulane.edu/apply/instructions/
Most Catholic schools are quite hospitable to non-Catholics, even atheists. I knew an atheist who graduated from Notre Dame and loved every minute of it.
So… having said that, your son might also consider Loyola University New Orleans. It is literally right next door to Tulane and shares dining services with Tulane. Some cross registration for classes happens as well. Perhaps he could transfer from Loyola to Tulane after a couple of semesters. Just a thought.
Loyola is a Jesuit school, and Jesuits are among the most tolerant of Catholics. The current pope is a Jesuit.