Originally posted by paw
Tetsutaka Sugawara has a series of books on this very topic. "Aikido and Chinese Martial Arts". I believe two volumes have been released and three are planned (someone please correct me if I'm wrong).
To the best of my knowledge, Sugawara Sensei travels once a year to the United States to teach. If you are interested, I can see when and where he will be in the US. (Any Katori Shinto Ryu folks lurking with better information?)
I have the two volumes you mention (the third has not been published yet). My own reaction is pretty much the same as P Rehse's. Very little factual evidence; much comparison and much speculation.
In some sense the problem is similar to that of comparing Shinto and Taoism. It is pretty clear that much of Japanese civilisation came from China, directly or by way of Korea. So if one were able to trace Japanese martial arts to their very beginning (with adequate archeological evidence etc), it is probable that China would figure pretty prominently.
Sugawara discusses Japanese culture and its interplay with China's and then discusses aikido and some Chinese arts. But we do not have any discussion of, say, the possible Chinese antecedents of, e.g., the training technique called 1-kajo / 1-kyou, for example, which is a fundamental waza in aikido and which came from Daito-ryu. It is possible that there are such antecedents, but this is a separate question from the question whether Ueshiba saw or practised Chinese martial arts on his trips to Mongolia / Manchuria. Aikido and Chinese Ba Gua might be similar, but it requires extra evidence to show that this is not a coincidence.