In this clip of Seigo Yamaguchi Shihan, at about the 1 minute mark, the uke starts to resist. To my eyes Yamaguchi Shihan struggles a bit and his movement becomes smaller and less smooth. I also think that the uke becomes very open (suki), especially his head. I wonder what the purpose/intention is to continue to do Aikido "technique" in a situation like this.
My own take on this,,, around the middle the uke appears to be getting strong... I noticed Yamaguchi talking while that was occurring. I think he was making a "don't do this, it doesn't work" example.
At one point he seemed to be walking around with his partner attached to his arm. Once again, my take was that he was letting the crowd see how hard the attacker was working... I've done that myself.
There wre a couple of instances in which the uke's balance was broken but he chose not take the fall. He was quite open in that situation. Out context it is impossible to know what was happening... was this what Yamaguchi Sensei wanted? Was it the uke screwing with Yamaguchi? Yamaguchi kept using him for ukemi the whole time so I think it was all fine with him and there were certain points being made to the students. Sensei's usually stop using ukes they think are screwing with them. Either that or they dismantle them...
I think the salient point is that the uke was never properly aligned when a fall didn't take place and Yamaguchi was in position to make whatever adjustment was needed. He certainly didn't look upset with the fellow... the talking seemed to be to the crowd