Peter A Goldsbury
I agree with David Soroko here. My teacher K Chiba spent some months in Iwama after he had a back injury and he also believed that atemi was a major aspect of aikido. (I believe the perecentage varies from teacher to teacher, but for him it was around 90%.) However, other teachers I have had did not stress atemi so much, in the sense that they did not do it as often as K Chiba. But they clearly realized its importance. (I am thinking here of Tada, Yamaguchi and Arikawa.)
Some Iwama atemi standards https://youtu.be/zQCVpC20MNg?t=135
.These are standards in the sense that atemi is in the kihon technique and taught this way from the beginning. The one I haven't seen until practicing for quite a while is the kick during entering into shihonage (to prevent potential leg sweep counter ).