Cause I found this cheetah-skinned cat not even a couple paces away from Far Watch Post in the Barrens and I checked on Petopia, they aren't listed under the cheetah skin.
It should be noted that there were only two under the entire tree, both level 11 (so I have no idea if they spawn any higher or lower, sadly).
I can't be the only person who's found these kitties... right? 
Edit:
Right as I posted this the one I killed respawned as a level 12.
So the known levels for these are 11-12.
Not sure if this should be mentioned, but there is also a cheetah cub following closely to the lvl 12. So this is one spot to get those once MoP hits.
Double edit:
I'm sorry if the image wonks out in Chrome, it's been doing weird things to photobucket images lately, idk. I'm not sure if it's still visible in other browsers.
)