Originally Posted by
alwaysbebatman
This is one of those cases where it's only a plot hole because you've decided it is.
What do we know of his vow? He described the vow, he did not recite it-- we do not know the exact wording. But what we do know? Hel, a rational actor acting in her own interest believes that she can force his vote by having the council Dominated by vampires. Is that because she believes she can hide the fact that they are dominated from the demigod? Or because she knows that his vow is worded so that it does not matter? We don't know yet. But we know that she must have a way to deal with this issue that she believes has a reasonable likelihood of success, or else she would be taking a different course of action.