Do you know where the clip was taken, or who the uke is?
The location is clearly a sports hall and not a dojo, so I wonder whether the occasion was one of Yamaguchi Sensei's trips abroad. To me, the uke looks somewhat like Minoru Kanetsuka (of course in 1976 this would have been well before the onset of his cancer). This is speculation, but if it was Kanetsuka Sensei, I know from experience (having often taken ukemi from both) that he would have given Yamaguchi Sensei a run for his money.
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.