When neither is religious, being of different religions isn't a big problem. I'm white, raised conservative Jewish. Hubby is Mexican, raised Catholic. Both pretty lapsed in faith, let alone specific religion.
I know of a couple, both white. She is devout Christian of some group. He was raised Catholic, even went to a seminary for a while. Is now not only atheist, but thinks religion is a crutch at best, and ridiculous. Yet, they have been very well together.
People also change, though. My dad was raised Catholic, but was lapsed by the time he married my mom and had us kids. He is now becoming much more religious again. My mom was raised in a mixed religious household, and was exploring different religious throughout my childhood, but is atheist now.
They are also divorced, but I think that had more to do with other crazy shit.