If you see a guy in a room full of mats execute iriminage (Do I need to show my list of credentials before I use this term?), then do you run up and ask him if he believes the spiritual doctrines of Uyeshiba before concluding that this guy knows some Aikido?
If I see a guy in a room full of mats executing iriminage, what I would first do is what his technique. If he knows good aikido, his physical and spiritual competence will be apparent. I do not think his beliefs are of concern to me.
I believe there is a difference between personal belief and competence. What you are hearing from several other posters, including myself, is that usually good aikido is practiced by aikido people that at least understand Ueshiba's spiritual teachings, even if they maybe don't share his beliefs.
I think that spiritual comprehension of the principles of is important to training and should not be ignored, just as I think that physical comprehension of the techniques is important and should not be ignored.