Hmm...

then can men qualify to give virgin birth ?

I believe dryads have only ever been women. So no.

But what about Ain? He's a quy and a dryad...

I think he's only inherited that one ability, which indicates he has that blood, but we'll see how the author goes about it. It'd be an interesting twist if he could get pregos, but most dryads stories I've come across say they're only females. But its all up to the writer author

it should be possible i guess since dryads are trees and they should be genderless, or ... both i guess?

I've actually come across this as well, it really all depends on the author interpretation. I've just generally come across dryads as these tree spirits who are like the land version of a siren.

True, in most cases are represented as women but are usually genderless, so that's interesting~
I was also thinking since dryard can create clones of themselves Ain could (have been) a form of clone since she used a piece of herself... but hear they all have clear genders so yeah! Can't wait for mooore~