Ueshiba insisted on suwariwaza so there was much more done when he was present. I hope there is plenty nowadays, it's one third of Aikido.
Sure he did - but if you look at what he actually did, there was less actual movement on the knee than there is in most modern suwari-waza. More than that, look back to Daito-ryu and there's even less movement - back before the prevelence of smooth canvas covered mats.
Regardless, the fact that he may have done something doesn't make it healthy for you. He also participated in static stretching - which studies now show to be ineffective at best and harmful at worst, and suffered from various health issues related to diet.