Players currently can't collect or do battle with any wild pets, so we don't know yet. It's also unclear which wild ones will be collectible, which ones won't be, or if they'll all be able to join our collections.
I'm definitely hoping we can collect them all and summon them outside of battles like a normal vanity pet! If not, then it would make wild pets less interesting for those who don't wish to participate in pet battles, and I just can't see Blizzard making it that exclusive.
Feel free to browse through Perks N Peeves
, my vanity pet collecting blog!