Ueshiba specifically stated that one does not have to practice shinto to do aikido. Some of his top students were into zen, others were atheist, others followed Omoto Kyo...it just depended on what they found in these different paths. I believe some of the words used by Ueshiba were "aikido is not a religeon...it unifies all religeons..." or something to that effect.
Ron (say, whatever happened to the spell check...I really need that little bugger... JUN!!!