In my dojo, I have christians, non-christians and some who don't practice any religion at all. We all practice in complete harmony with one another. I've had at least two students say to me they joined my dojo because I was a Christian. That's cool! But we keep such conversations "OUTSIDE" the dojo as to not exclude anyone from our training time.
This is true for my home dojo as well. I think this is possible because those of us who practice Aikido in the Yoshinkan, do so with the understanding that Yoshinkan is not a religion. It is a the unification of the mind and body through our repetitive way of training.
In my school, when we speak of one's spirit, we speak not of some mystical being we can't see or touch, but rather all those things that make us who we are as individuals. To make your spirit strong is to bring your mind and body together as one.
So for those who train at my dojo, it is not a problem. In my opinion, you alienate a large number of people when you start talking about religious and spiritual things that fall into conflict with many other religions and peoples beliefs. And if you create that conflict, then your not doing a real good job of teaching Aikido. (IMHO anyway)
Well, that's my nickles worth anyway. No offense intended ....