I don't really like it. It's very common, but still only makes me think of
Ethan Hawke (I don't like him much). I don't think that
Nathan and
Ethan are too similar. I think it would even honor him a bit and be nice. Plus he'd always be dad or grandpa anyway.
Evan is feminine to me because I grew up with a female
Evan. I always thought it was a variant of
Eve and
Eva and it never occured to me it could be a boys name.
I would say I like
Evan and
Ethan about the same.