Guild Wars isn't just for kids though. No doubt, there's a chance he could meet some strange people in the game, but I'm sure that as long as you monitor some of what he does, talk to him about it, ect, you'll have nothing to worry about.
These people don't sound like they're pushing Christianity on anyone. I'm a Christian (southern baptist) myself, and I hate it when people try to force Christ on others.Yelling a point over and over or beating someone over the head with your point will not improve your chances of getting someone to think about what you're saying. It's a choice and if you "force" someone to choose, they haven't really chosen.
This group sounds interesting, I haven't played Guild Wars in a long time, though I love to drop by every now and again. It's the only MMO I play, and while I'm not really into joining guilds, I might look these guys up just so I have someone to talk to occasionally, about God and about the game. I like what they're doing and I hope they continue to thrive as a community.
Oh, and also, Guild Wars isn't like your normal MMOs. If you're looking for one your son can play, this would probably be a good bet. The only fee you pay is to buy the game the first time, it's free forever after that. It's fun and interesting, there's a great community, and it's more story based then games like Everquest. When you're on the game map, you're only in contact with the people that are in your group, so if you're worried about your son meeting lots of wierd people, that only happens in towns. Even then, the community is such that strange people are rarely encountered. (Random dance/ invisable musical instrament sessions do break out from time to time
.) I'm not a fan of MMO's, but I actually enjoy this game as it's really fun to play, and not taxing on your computer either. Hope that helps some