Yeah dude, Vergil is always grateful to people going out of their way for him. Sparda did teach him manners, after all. And he always pays his debts, so look for him to be helpful to Alastor for doing things like letting him crash at the castle until he finds a place, or making the sword. If there's anything Alastor needs, he can basically ask Vergil and it'll be done.

(Oh? :o)