Trying again...
If you do a search on this, you will find a lot of good answers, since this has been discussed before. I just found a bunch of links, but the Comcrap lost them, like it always does. Let me try again for you!
Christianity in Ritual
Joining a GLO and not being religious
Greek Acceptance in Church
I know there are more posts on this, but my searching ability is not tip-top.
From personal experience, my sorority is founded on religious principles (our open motto, "Founded upon a rock," is a Biblical verse) but I know there are atheist members of my organization who are still very comfortable with our ritual.
Threaded Mode