Mirrors in the olden days were made with silver, and because silver is the good pure metal it refuses to reflect the evil vampires, hence the lack of reflection.
Modern mirrors lack silver so they will reflect vampires just like everyone else!
Evil is the state of being without the grace of God. His grace may save someone from evil, but by a any reasonable definition of morality those without His grace are evil, whether they're aware of it and reject it or not, as all good flows from Him. (I don't believe any of this.)
Isn’t it evil enough that you don’t avoid evil actions? Is it necessary to take it a step further by intentionally favoring evil actions or even restricting yourself to exclusively evil behaviors.