well Saladin and Richard Lionheart thought about a marriage alliance. It did not happen as there were a lot of opponents to this due to religious reasons on both sides.

Also in austrian history there are some examples where catholic heirs and princesses were married to hungarian and bohemian heirs and princesses with weird manners that were considered heretic by most of europe (if you can call living in a tent with lots of female slaves, spending your days getting drunk and smoking some herbs, heretic...)

Politics and money stand above religion. Just that they sometimes have to arrange with the pope to ease their stand...