So this covers all the Tick media. Mostly the first Live Action series. I know the Tick is often presented as an amnesiac but I think the episode where Arthur has a girlfriend and Tick is completely unable to understand it proves Tick is not human. He barely comprehends human language and often hears "Blah blah." from people. Granted yes he probably does have the head injury thing but I think the scene where he sort of understands what's happening to Arthur is the proof.

He spend the entire episode trying to understand Arthur's situation (dating) and it takes seeing a segment on a Praying Mantis for him to get some semblance of understanding. Even then he begins believing that Artur's life is in danger. I also noticed in this episode his antenna's move. Particularly when he's thinking, and I suspect this is an indication that he's a alien. from the antenna's to the bug video thing the only thing that could explain to him.