I'm an agnostic atheist who is open minded to spirituality though lean towards being skepitcal of it all despite my fascination with mysticism. In any event, yes I would date a theist. Someone can be an intelligent and amazing person no matter what diety they subscribe to. There are all kinds of people out there. What's important is their social views and whether that would impact our relationship. If they were anti-gay, that would obviously create issues. If they were against scientific education, my future children wouldn't get the education they deserve. Things like that have an important impact on how stable our reationship will be. We would have to have some common ground to ensure it would work. However, their religion and faith itself doesn't need to cause issues. It's about who they are and not what they are. I will say though, I would have a very hard time if they were devoutly catholic and wanted to raise my potential future children in that system. It brings up to many bad memories and fears. While I don't know all the details and this isn't related to my direct family, I had a family member that was an alter boy who was abused by a priest. The church simply moved him to a different church and my non-immediate family continued going to the church that caused so much grief because they are very religious. In turn, my family member struggled for the rest of his life to get over this crap. I can't ever forgive that institution for that nor can I understand the blind devoution my family showed in return. Again, I don't know all the details, but it absolutely disgusts me. And I had my own set of issues and difficulties with the church as a kid myself. I don't want my future children to ever be a part of that system, so that's my blind spot I would have a hard time negotiating with.
One thing I will say though is that true love should have no barriers. Opposites can and should attract if they are meant to be. I have a hardcore atheist friend who fell in love and married a deeply devout catholic girl. They are madly in love and very happy with one another. And isn't that what matters most? I'd rather remain open minded in hopes that I'll one day for the right guy for me, whatever religion he may be.