I don't know how much the kingdom and the dragons talk, but I guess everyone in power knows about him being a vampire now.
He's not a vampire though (even if he keeps saying it). He's a human with the skill nightmare daywalker (daywalker apparently being vampires who don't fear the sun) which I assume is why the dragonlord refers to him as a strange king of the night.
Apparently, thanks to the skill, he has the same power as a vampire which at the very least involves healing lethal wounds and large boosts to his physical abilities. His fangs, nails, ears and eyes all change a bit. When he drains people, they turn into sludge/crumble away or, according to the dragonlord, if they are suitable they actually get turned into a vampire.
So yeah, he's got a skill which could turn one of his enemies that he's draining into a vampire. That's pretty cursed. I guess the good news is that it's not that simple to turn someone into a vampire so he won't unleash a vampire apocalypse by mistake, I think. On the other hand, if he ever successfully turns someone, that person will be more dangerous than before he turned them. I think he can avoid using drain if he hasn't sustained any injury and just kills people using his enhanced physical abilities. We'll see if he actually understands that the next time he uses the skill.