Dark elves just get 24 percent dodge from familiar agility. But I find any dodge is quite significant and simply having the skill seemed to make my evade fire more often. Evade being what it is though I could be imagining that.

Also cat is a relatively frail familiar. You want your familiar to survive aeriatoma's gas attack, you probably need homonculous, which iirc is the toughest of the neutral familiars?