Honestly I'd say that they just would straight up be immune. If they don't have a brain then how would they even process the hypnosis? HELL HOW WOULD THEY EVEN BE ALIVE.
True they probably wont have the capabillity to even know whats going on.
But amoebas exist and they dont have brains. And with fantasy creatures like slimes and skeletons I think theres a little magic involved