Can Hags give birth to boys? Also, what do you think of this character concept?

Ahem. HexBloods. One origin option is "A coven of hags lost one of their members. You were created to replace the lost hag." and both men and women Hexbloods were shown in van Richten's so it isn't a stretch to say the hags created a child, it turned out to be male and they didn't want it. 
So if you want to stick to lore, there you go.

But you don't have to stick to lore. My Hexblood was kidnapped as a kid, was being converted, when his parents who were retired adventurers broke into the coven and reclaimed their son. So what if he is a little weird now and one of his eyes looks constantly bloodshot? Yeah he might hesitate at church entrances before going in, phrase things oddly, and sets off divine sense in paladins, but he is still a good boy.
Talk to your DM and see what they will agree with.