Stepping into waters I know nothing about but... is that a Pirahna nibbling at my toes?
I remember being at a small New England dojo a few years ago where Chiba sensei was giving a seminar. During one of the breaks a pair of senior students were doing kumitachi. I remember thinking (and this was after I had already read all the comments regarding aiki-ken - nothing new has been said) that it looked vey much like the Shodokan kumitachi which does not come from Ueshiba M. but from Tomiki's (and Ohba's) ken background. Both these men were 8th Dan in Kendo and over here that means much more than heat frustration.
I spent a short time learning TSKR kata and am now spending quite a bit of time on the Shodokan kumitachi. My initial impression is reinforced - I don't see that much of a difference. I haven't seen the Iwama stuff performed by anyone I knew that knew their stuff so I can't comment.