I've only seen Saito sensei "in real life" (outside of video tapes and such) but it seems like his approach to aikido does include atemi. Can others add to situations in which Saito sensei uses atemi in his techniques?
I never got to feel Saito sensei at his seminar, but Isoyama sensei did use me as uke at times during his seminar. His techniques are very precise and effective. I wrote a review
of his seminar which should have my experience at his seminar.
It's tough to "compare and contrast" their aikido as I didn't get to feel Saito sensei's aikido. Isoyama sensei's aikido seemed different externally from Saito sensei's, but how it looks is often not an indication of how it feels.