If it was a mindless undead, then I could see that you might decide you want them to be immune to some attacks vs Wis/Int/Cha, but why this one and not all? As the target was a vampire, it clearly has a psyche and will that can be attacked and overcome, so what makes it special to be immune?
The things that irk me a bit at my table is hold person being used on Draconians with tiny wings, or mutants with 3-4 arms. It kind of feels like having an extra limb should not make you immune to a spell, but if you allow that, then where do you draw the line?
P.S. Oh I had not read the word Humanoid as a Keyword, I just read it as a word, hence the rather different views on the topic.
