The hunter might not recognize him because he meets Astarion during the day.
Any monster hunter who lets their guard down
so completely that they don't recognize their vampire mark - red eyes, pointed teeth, pale skin and all - simply because it's daytime is a monster hunter who probably won't live long. And this one doesn't.
I wouldn't be as invested in a redemption arc if our selection of male love interests wasn't limited to Gale, Astarion and - apparently -
Which, if Astarion is purely and forever evil, just leaves my all characters playing tug-of-war with Mystra over Gale. I'd like at least one other option.