Would the hunger affect normal humans? And what if someone from another universe (Fell Papyrus, for example) entered the Axtale universe, would the fact they're not from that verse make them immune or resistant to it or would they be affected like anyone else?

Anything with magic would fall victim in time, same universe or no. Humans take longer, because the magic of their soul is protected inside their physical form, but with enough time they would, yes.