Here's an interview. He mentions some of the things that I mentioned earlier. He seems very down to earth about Aikido here. A bit to spiritual for me on some of his videos but I think, I get it. A lot of what he describes seems more like how Athletes "get in the zone."
I don't know if he sparred or not but some of the things, he says are some of the same things I've learned through sparring. From the little bit that I watched from videos it seems that at the very least he has worked against resisting partners. To be honest I don't think one can flow without experiencing resistance. I can't learn to learn to feel the change in flow without resistance.
When I do push hands, My goal is to detect resistance and to hide resistance at the same time. But either way, it can't just be one person yielding all the time.