I don't think Sims should fear Vampires by default, but I do think a Vampire's actions should trigger it. Like when they feed without permission. That's an aggressive act from a Vampire and both the victim and bystanders should freak out. Some Vampire powers and weaknesses should also inflict fear, like Uncontrollable Hissing.
And I think certain Spellcaster spells should inflict fear or terror. Setting someone on fire or electrocuting them should definitely trigger it. And when a Mermaid tries to drown a Sim they should panic.
I just think it needs to be incorporated a little better with Occults, and Occults should have an immunity to their own fearful acts.