This discussion could be resolved fairly easily. Take out the atemi and practice with a partner who has no intention of cooperating.
Saotome Sensei, who had fifteen years training under the Founder, stated that "if you know that your partner will not strike you, then all techniques are stoppable".
All techniques need to be appropriate to the specific energy given by an attacker. If the attacker knows there can be no atemi, he can shift his energy to make the aplication of any technique impossible. Normally, if the nage has moved correctly and is in the proper position doing this would create a suki and leave the attacker "open". But with no atemi the question would be: open for what?
I remember, one of the last times we had this discussion, Goldsbury Sensei corrected those that had maintained that Aikido was 70% or 90% atemi by pointing out that it was, in reality, 100% atemi.
Saotome Sensei taught us that "every throw you do is a strike which you are choosing not to do." In other words, in Aikido practice, atemi can be implicit rather than explicit. What forces an opponent to keep his energy dispersed so that you can apply a given technique is the possibility at any instant that nage can throw an atemi.
If you make some artifial "rule" that there is no atemi then Aikido is simply a dance like contact improvisation (also where there is no atemi). There would simply be no possibility of application of technique against a trained attacker. If you don't believe this then try it out. This isn't mysticism requiring many years of esoteric training. Just get an experienced partner, preferably one who doesn't share your own predisposition, and try it out.
As for some teacher or other banning atemi... I have hundreds of hours of video in my collection. I have video of Koichi Tohei using atemi, Kisshomaru Ueshiba using atemi, O-Sensei using atemi. Perhaps Tohei Sensei decided, for his own reasons to deemphasize the use of atemi in Aikido practice, but it was there in his technique.
Just look at the people whom O-sensei trained directly... certainly no one from the pre-war era maintained there was no atemi in Aikido. Of the post war era teachers some of the most notable would be teachers like Saito Sensei, Nishio sensei, Hikistuchi Sensei, Saotome Sensei, Chiba Sensei, etc. For every one of these men, atemi is an integral part of their Aikido technique. Is anyone out there maintaining that they all got it wrong? Somehow the whole bunch of them failed to understand the Founder and that a particular individual who may have chosen a different path was the only one who did get it right? I am sorry, I just can't buy it. But once again I say, don't take their word for it. Just practice with ukes who will throw combination attacks, who will resist your throws, who will tighten up when you try to apply a lock, or will slip any attept to grab them... then see.