I have been on the mat with Seagal Sensei, and taken ukemi from him.
What he does is very much real. One of his influences (and the person that recommended him for nanadan) is Isoyama Hiroshi Shihan who is know for is powerful technique.
Seagal Sensei is real.
I still wish Isoyama Shihan would have made it to the Aiki-Expo. I would love to take ukemi for him, or at least watched.