I think psychohistory is certainly not dialectical, but i don't know that that means Asimov is anti-dialectical though. Marx use of dialectics are an admission that the sort of reductive analysis that science relies on isn't possible on a society. You can't easily cut society up and analyze part of it in a vacuum. I think Asimov asked the opposite question (instead of what do we do if we can't be reductive) he asks what would be needed to be reductive. Hari Seldon is given everything he needs to do that. He gets access to a robot who has access to history long since forgotten, and who is capable of reading and manipulating minds, and who has done so for the purpose of changing history. He further had access to all of the psychological and mathematical knowledge of the empire.