While I've not read the entire book, I've read the sections in question.
The information isn't substantiated at all. In all the records I've read, written by his students and son, Ueshiba never gave any mention of study in Chinese martial arts. This leads me to believe that he did not study Chinese martial arts. In most other regards, Ueshiba seemed happy to give credit to his teachers where credit was due.
There are similarities between Chinese martial arts and Aikido. This isn't any more signficant than the similarities between Graeco-Roman wrestling and Judo.