For Agron(/Nasir) - what if Spartacus was a prey who freed other preys? So like, they went around killing vampires to free the people bound to them.
Korra could be a hybrid if she was born from a vampire-human couple, just sayin'.
Bull could be someone who arrives to town through his travels, and then you can keep the actual Qun/Tal-Vashoth lore as it is??? Surprise, Qunari exist in some remote area in this world.