Re: Other suburi than Iwama
Takeda Sokaku spoke about this connection, and Takeda Tokimune writes quite a bit about it (see Aikido Journal). It's almost surely true. FWIW, there is, however, no independent record or recollection of this within Jikishinkage-ryu, whose enrollment in those days was quite large. In Tokimune's writing, Sokaku is described as a very significant member of the school, during his period of enrollment. It's possible that he was there, but not nearly so prominent as his son describes.
Similarly, Wang Shu Chin claimed to be a student of Chang Chao-Tung, one of the greatest of bagua instructors. He was not recalled, however, as an indoor student - rather, it is more likely that he just attended Chang's classes as part of the "crowd."