Morihei Ueshiba was a ardent oomoto-kyo follower. Rumours of him bullying his students to check out the religion abound. Ueshiba claimed that oomoto-kyo was inextricably linked to him developing Aikido.
How effective was the spread of oomoto-kyo within Aikido?
In shodokan Aikido, you would be hard pressed to see any evidence of the religion as far as I can gather despite Tomiki dabbling in oomoto-kyo at Ueshiba's advice. But other style (ki-aikido, I am looking at you) might be different.