Did you happen to meet any current students when you interviewed there? Can you contact them and get a feel for what the other students are like? Or perhaps any other interviewing students that got in there, too? You probably don't want to come out to them, but maybe you could indirectly see how their political/religious views are (Facebook could be a good source for this...).
Some Christian groups are more into witnessing to non-believers than others. If that would really bother you, maybe you could get a feel for that by contacting them. From what I've noticed with family and friends who are Christians, those who tend to put a lot of Bible verses/mentioning God or Jesus in their every-day letters and e-mails tend to be more into witnessing to people and usually more bothered by homosexuality.
Also, do you think you could find a community outside of the school that you could fit in with better? Did the school feel comfortable in other aspects?
If the school is against homosexuality in any official way, i.e. if it would violate the code of conduct, I wouldn't go. Four years is a long time to hide that aspect of yourself, and if the school is that bigoted, it might start to drive you crazy. But if you can't get kicked out by it, and the students seem like you could get along with them, I'd probably go for it if I were you.