If you search on Youtube, you can find footage of Seagal performing randori during one of his dan tests. No doubt, he's a legitimate aikidoist.
Take Sensei is indeed a ligitimate akidoist and if memory serves he was one of the few westerners allowed to teach in Japan. His aikido is what some have refered to as "severe". I have seen interviews on tv and dvd and from what I could gather if you attained a shodan from Take Sensei you were put through the ringer so to speak. I believe he adapted some of the technique to be more practical and applicable for self-defense. I'm sure being over 6ft and 200+ pounds didn't hurt his Aikido either, that combination with his ability equals quite a formidable person. Also, I have spoken to some people who have trained with and taken seminars(I wish I could have) that he is very down to earth and approachable.