Noctis would be happy to support Alucard! Since Noctis has an injured arm he's better suited for back-up and info; he knows how to keep point and can encourage him to favor stealth over... you know... inadvisable brute force. That and he can teach him how to use guns and give him Pro Tips, which would be handy.

If Alucard does end up bloodied then Noctis is pre-hurt and ready to help him figure out his abilities, too. (plus there's a great chance of Ignis and Prompto hanging nearby so this is like a three-for-one deal here, potentially)