Hmmm. o ^o This brings up a good point. There are a few Size-modifying Passive Traits (which can affect battles)... I guess it's not unreasonable to make a few more Passive Traits that can affect battles, especially if I make Battle Traits that mirror their effects.
Okay, so I've looked into things, and here's what I've thought up:
Blind – (Negates Chameleon Skin, Razzle Dazzle, Pollen Spores, Spit Poison)
Deaf – (Negates Horrific Moan, Horrific Wail, Sonic Waves)
Tactile Anesthesia – (Negates Freezing Touch)
So I could easily just make three Battle Traits that do this and say that a pet with any of these Passive Traits automatically gains the respective Battle Trait.
However, I also noticed that there could (should?) be certain Battle Traits that gain a bonus against pets with these Traits or (more importantly) Battle Traits that pets with these Traits should not be able to take. I'm not sure how most people would react to the first idea, as Passive and Battle Traits have generally been kept separate, but I do think I should go and put some restrictions to take care of the second idea.