The Twitter account isn't verified, but it is linked from his (apparently) official website and verified Facebook page so it appears that it's his official Twitter account.
However I don't believe it's him posting. I notice "he" is also very active posting on Facebook, it is more than likely an assistant or a company in charge of his social media pages that do the posting.
Very few big time celebrities actually are 100% in charge of their social media profiles, they have entire companies and managers whose job it is to maintain an active social media presence.
Seagal doesn't strike me as a guy who would sit in front of a computer answering countless fan questions and interacting with strangers.