Templar Jesus magic isn't very well explained as far as lore goes, and some people think the whole "Aedric" thing is a sham. Regardless, the concept of Templar Vampires is quite contradictory no matter what way you slice it. I laugh at the absurdity of it the same way I do at a "Light Side Sith."
Personally, I think they should do something like what DCUO does with their Celestial power. With weapon attacks, the heroes are textured gold and white, while the villains are textured black and purple. Templar attacks (or hell, attacks from any class minus NB) with vampires could be textured black & red, like something similar to the attacks daedra sometimes use. I don't know if this would be possible or not, but anything to give the abilities a more corrupt feel to them would be cool.