Fascinating! I would tend to agree that it's very *hard* (not impossible, but hard) for people of different faiths to have a strong marriage. I guess it depends on how strongly they adhere to their religious text, because if they are a literalist most religions will say "if you're a nonbeliever you're going to be punished" and thus someone who loves their partner who truly believes if they don't convert they're going to hell, they will constantly be trying to convert their partner and not be satisfied with "agree to disagree".

There is a friend of my husband's who is an atheist, whose wife is an Evangelical Christian. Guess what, she tries to convert him all the time, makes him go to church, until he felt pressured to convert even though he didn't really want to. Now he feels a sense of resentment. Not a good feeling in a marriage.

If however the religious beliefs are more "this is my belief, and this is your belief, but at its core we believe similar things and our preferred rituals and myths are different" I would say it's more likely to work.