Re: Using Ki. Ki-atsu.
Yes, I do ki-atsu and have been using it to good effect for over 15 years. I mostly get called on by students who have a minor injury, sometimes picked up during practice, sometimes not. I also sometimes offer it to work colleagues if they have any aches or pains that are giving them gyp. Just about everyone reports an easing of the problem they are having. Which is good, as I don't guarantee any cure, only that "it may help".
How does it help in aikido? I can't say that I have even thought of it like that I just see it as an integral part of what I do.