I do not believe that Alex is in any way Ethan.
From what I could gather, who in the hell takes their kid on a journey like that one? Really?
I think that Rousseau was the boat's Claire. I believe that the boat wrecked because she was on it, and pregnant. Then, when she was about to give birth, these people abducted her and took the baby to raise on their own. This island has some way of taking these children born there...or something. The psychic thought he was getting rid of the problem, but he was in reality facilitating it. Perhaps he hadn't seen the events after the plane crash, but simply the crash itself...who fucking knows, I give up.
I think Claire's baby and Alex have some sort of tie...and Tom Cruise's cousing is too old to have been there for only 16 years, if my baby born on island theory is correct at all. Which is highly doubtful.
I love this show.