Don't forget that Ueshiba study Judo under Kiyoichi Takagi from 1903 to 1908 when he was calling his marital art Aikibudo.
I have never heard of O-Sensei using sutemi waza, but the sutemi waza of the yoseikan are all the direct inventions of Minoru Mochizuki. Some people say that he got them from gyokushin ryu jujutsu, but he never actually saw the gyokushin sutemi waza. He was uchi deshi to Kyuzo Minfune, who was an expert at sutemi and he used Mifune's example with hints from his experience in gyokushin to develop a sutemi version of pretty much every aikido technique he had learned.
If you have any examples of O-Sensei's using sutemi waza, it would be interesting to hear about that.
Best to you.