Oscar,
I don't really have much to add to any of the above. I do pretty much agree with what Dan said though, like he said I would.
The concept and term aiki is older than the ajj use of the term, but mostly in sword schools, such as Kashima Shin ryu (which also contains jujutsu and very "aiki-esque" techniques in both the sword and jujutsu). There are other terms for what is being called aiki, in all of it's varied forms, in many styles. As you have no doubt experienced, Shindo Yoshin ryu contains such but does not call it aiki. I have seen very similar "aiki" technqiues to those of Daito ryu in arts that have no connection to Daito ryu at all.
"So how many licks does it take to get to the center of a tootsie-roll tootsie-pop?... The world may never know."
Richard Elias
Takamura-ha Shindo Yoshin ryu
Yanagi Ryu