Quasi
Steve knows Tony is not Howard.
At the beginning he tends to forget, it's easy because the two men are on first sight rather similar, in both mannerism and looks, in their genius and mad scientist-like disregard of personal safely and rationality. And before Steve manages to get to know Tony better, the memories are still fresh and painful and give him nightmares.
Tony does the same arrogant but brilliant scientist impression, charming the crowds, causing scandals, not listening to anyone. He's impatient and driven the same way Howard was, only a bit more reserved, probably because he's older than his father was when Steve knew him – and that's a confusing thought.
He owns SI and makes the world a better place. He drinks a lot, but he is not an alcoholic and Steve has learned enough of Tony-handling to know that if something was slipping out of control, Tony would tell him. He used to sleep with all pretty girls, but claims he's grown out of the phase a long time ago.
Steve knows Tony is not his father. He is a lot more.
(He is dirty mouth, blue light, sweet kisses, tired eyes, demons, that small crooked smile.)