How do you move the pelvis? How do you mirror your pelvis with the other man's pelvis? What is the offensive hip and what is the defensive hip? And how is moving the pelvis a well known concept in Aikido? Where has Ueshiba or Shioda or Tohei talked about moving the pelvis?
Well to answer most or your questions you look and learn about Sumo technique, there is loads of info on the net and on youtube. The O'Sensei question, I don't know. He could have talked about it in his poems, but am not an expert in interpreting his poems. Don't know about the other senseis but you will have to ask their students and look at their films, and do that research. Also that would be a great topic for another thread. But the topic of the thread is what can we learn from Sumo.
My question's purpose is that it has been said and believed that all martial arts come from Sumo. I am not an expert on Japan or Japanese language to pin point meaning or context of this phrase precisely if it was literal or otherwise. But for the sake of being a western minded person and with the use of observation I see similarity. I am not sure if they are intended or not. But they do exist, and it can be debated to what level or degree it exists. It is plainly obvious they do exist. It may not be to everyone, but that is the purpose of the thread; to explore that.
My kindly suggestion to you would be to answer your own questions present your findings. And I will be glad to discuss them here affording them an open mindedness and affable manner.