No, vampires don’t show up in mirrors, he’s actually in the mirror. In the TV series he has a habit of spying on watching Integra from reflective surfaces.

Alucard: What am I doing here? Looking out for you and the police girl, of course.
Integra (thinking): If I button up my shirt, it’ll look as though I’m trying to hide. I can’t look like I’m trying to hide from a vampire.

Integra: You don’t need to look out for me all the time, you know.

Alucard: [completely ignoring that] Seras and Walter were wrong, by the way.