Noticed this video of Takeo Nikishido on YouTube:
Bearing in mind that there is a lot of hokeyness involved in many of the demo's and the Uke's tend to be dive-bunnies, I'd have to say that Takeo Nikishido at least exhibits enough to tell me that he indeed has a very good grasp on how to use ki/kokyu-skills to do "aiki". Not that I'm judging from on high... I just mean that there is enough information via the video to make me personally feel sure without being able to feel him personally, etc., to make the call.
T, Nishido was a student of Kodo Horikawa, and of course Horikawa was a student of Sokaku Takeda. Interestingly enough, at least to me, Nikishido appears to enjoy playing with the "aiki" manipulations in very much the same way that Gozo Shioda does in some of his videos. And Shioda supposedly had *some* training under Horikawa, also.
Using the above information, I'd back-interpolate differently that Dan Harden does but arrive at the same conclusion... the bulk of Ueshiba's skills in "aiki" almost certainly derived from Takeda, although I'd hesitate a bit before I'd say that all the ki-training methods came from Takeda. And the ki-training methods are important; there are a number of methods to training these skills and Ueshiba appears to use the more classically "soft" approach than I personally see in most of the DR experts. But that's a personal opinion based on my own background.
Still, it's interesting seeing someone revel in "aiki" tricks in a way that compares to (but is showier than) Shioda's.