I'm curious, did O-sensei demonstrate this and have the class of students then train this way? I've never heard documentation one way or the other about this.
I would consider the fact that this is such a central aspect to Iwama style aikido to be evidence that he did. Further whenever I was able to train with Kurita Minouru Sensei (one of the last uchideshi of OSensei, who spent a great deal of time with him at the very end of his life) he always emphasized this kind of training at some point in the seminar. He explained it as a stage one needs to go through.