Arelith

As far as I can tell, rats are currently not counted as vermin with respect to Cleric - Plant - Vermin - Turn Undead.

Should rats be included in vermin or is the current classification intentional?

Vermin is a subrace category that includes spiders, crabs, worms, snakes, etc.

This is a base game categorization and not an Arelith specific one.

IIRC vermin (spiders/snakes) are not Animal-Empathy'able.... meanwhile.. you 'can' use empathy on Rats.

Making them 'vermin' would also drop them from Animal Empathy list

(not that this is a reason for not moving them, but simply an observation)

Since we have haks, why not make them be both?

Snakes are Animals in base NWN (and on here) but are Mind Immune which is why Animal Empathy fails. Some spiders are Vermin, others are Magical Beasts and thus Animal Empathy will work on them.

You can technically split them even without haks, as I know some drakes have both Dragon and Animal levels in the module and thus can be affected by Animal Empathy.