I don't try to be familiar with all martial arts so I don't know much about Daito ryu, even though my art is thought to have a connection with it. For the same reason I can't confirm nor deny that it and Aikido are very similar. It just doesn't sound right. As to Dim mak, I think that has been discredited already.
For the founder of aikido, Morihei Ueshiba, as well as his early students, they were pretty much the same thing. In successive generations, the mainline art was heavily modified. It's well-documented so if you're interested there's lots to read on this issue.
I know there are several styles of gung fu where the practitioners invite spirits to possess them...
Research Notes: Spirit Possession in the Southern Chinese Martial Arts.
I believe there are some Silat systems that do this as well.
If I'm not mistaken, it's relatively common in koryu as well. Ueshiba also practiced it extensively for both his spiritual and martial training (getting possessed by "gods"). Some of this knowledge has been passed down, although the exercise here is pared-down (scroll down for the English version): Chinkon, expliqué par SAITO H. Sensei - Aikido Blog (.net)