I would think Declan could become a vampire, if he was willing, but it’s up to Mr. Conroe whether it happens or not.
It was mentioned in Winterfall (IIRC) that dragons naturally used magic to fly & that may confer some immunity to “our” type of magic. It’s not total immunity obviously since Declan used fire & lightning to zap Trygon.
I believe most weres are half-n-half blue/green & Chris noted Nadine’s mostly green with surprise. It may be due to her father being a shaman or a result of her link with Director Stewart intensifying her LV. Chris’s blood & aura may just have streamlined Stacia’s LV to make it more efficient. A better strain, if you will.