[Opinions] Re: Evan (girl)
It's definitely usable, but in the same "mostly-male-but-used-for-a-girl" way as Hunter and Tyler.
That being said, I would much rather see Evangeline with the nn Evan. I personally would only use Evan on a boy (I really like it for a boy!).
Evvy is just awful. If anything, I suggest using the spelling Evie or even Evy.