My dad is Catholic, and my mom is Methodist. They've made it work for (Oct 21st) 47 years now. Mom serves, and eats, only fish on Fridays...or at least non-meat dishes. They have different schedules for going to services, so dad goes early and gets the donuts on the way home, and mom has breakfast ready when he gets there, then she goes to hers. She was more adamant than dad about me going through Confirmation because she'd signed papers agreeing to raise us girls all as Catholics. None of us stayed in that faith as adults.
Now, I'm a Pagan, my younger sister is Methodist and the baby is Southern Baptist.
Although I prefer not to date anyone who belongs to any organized religion, I can if they're open-minded enough to accept my beliefs. My current bf says he's Baptist because that's the church he was raised in, but totally understands and shares many of my beliefs...and is educated on and interested in the rest, at least.
I think it can work if one respects the beliefs of the other. Not one of my marriages ended because of religious differences.
I have been married in the same faith when I was still Catholic, married to a fellow Catholic who switched to Methodist with me for the years we were together so that we could get married (Catholics don't recognize divorce and we had a baby on the way), and to an Atheist who married me in the Methodist Church to make me happy. My last one was Pagan to Pagan, but I always called him a Pagan Agnostic. However, we did a Handfasting first, which is the old Celtic ways and not a legally recognized marriage...but we got a certificate that states that day we were joined as partners in love and life. And our vows made promises much more in depth than the normal ones. A year later we got legally married because he was sick and needed my health benefits, and toned the ceremony down a bit from its Paganism out of respect for our Catholic fathers, who were both in attendance.