Correct me if I'm wrong, but I believe part of the reason Ethan was able to do any of these things, or survive past the beginning with Mia was simply because he too was also partially infected as well. His hand being sewed back on was done by Jack after the confrontation with Mia in the attic, or at least that parts implied heavily. You can only see Evelyn (at least the hallucination of her) if you're infected, and considering how virtually indestructible the Baker family is when the infection fully sets in fully, well you get the picture.
You sort of have to allow some suspension of disbelief in a series with biological monsters running around. Ethan is still pretty 'normal' compared to most of the cast of the RE games.