قمر

I say this, but I'm not saying that Vergil would be a great father. Vergil has truly shown that he does not despise his family entirely, he definitely holds resentment towards his brother but he values his kin just as much as he does Nero.

briefs

In DEVIL MAY CRY 3, between the fight between Vergil and Dante, Vergil valued Dante's life over his own. He demonstrated this by not only having playful banter with his brother(showing that he still has fun), but slicing Dante's hand to prevent him from falling with him at the end. Vergil may not be a decent person, but he's definitely selfless to an extent.

In DEVIL MAY CRY 5, Vergil shows just as much, if not more, acknowledgement and care for his family. After Dante revealed to Vergil that Nero was his son, he kind of... always knew another one of his own flesh and blood was out there—

((WELL WELL... THAT WAS A LONG TIME AGO.))

—it may not have been upfront in his mind, but it must've always been a lingering thought in his background.

During M20, the fight w/ Vergil as Nero, prefight was Nero's monologing about sibling rivalry and settling differences. When Nero asses that—

((NEITHER ONE OF YOU ARE DYING HERE.))

(smth like that) Vergil, albeit subtle, gives a very impactful nod. This alone indicates that he does acknowledge his family in a way he hadn't before, that he truly does care beneath his abrasive front. He really does acknowledge Dante as his brother, and Nero as his son. This is his family.

theory

In MY opinion—

If Vergil knew about the pregnancy beforehand, he would've stayed. The man went mad in his persuit of power, power-hungry and blind to his own weaknesses. If it were different, if he had stayed with the woman, he would've taken care and raised Nero as his own.

He was young, so he would be confused and doubtful about raising a baby. I believe he would've slowly gotten used to the idea, and grew into his own parenting style, even if the mother wouldn't want to stay. He would want Nero to be just like him, he'd start introducing the boy to weapons near his teen ages, I'm thinking. They would train together, Vergil would even push Nero to train without him until he felt stronger. Until he could break a boulder with his bare hands. It would eventually hurt Nero, surely, but Vergil would call it progress. This would make Nero eager to recover and more confident in his strengths.

and Vergil would be a proud father.