there is a ram that comes in as a second pet in the wetlands that is full sized and non captureable
This is a known bug and will be fixed sometime in 5.1, according to patch notes, starting with Gazelles.
You can read about some of my documentation on them [url=http://us.battle.net/wow/en/forum/topic/6794641141]here[/url], if you like.
Edit: Wain, you can add Wharf Rat to the list, perhaps? These have an extremely low chance to spawn in Booty Bay (as primary spawns) and nowhere else (in spite of the tooltip claiming Tol Barad), and have an extremely low amount of spawn points, to boot. Plus, they appear to compete in spawn points with the non-wild critters and wild pets that crowd the wharf (such as the crabs and roaches). You're really far more likely to see them as secondary/tertiaries--and I think either they're still bugged, or they were only recently fixed where they weren't even spawning in Booty Bay, thus available only this way.
I know they still won't count on my achievement like the Crimson Moth, either, come to think of it. I wonder if there's a relation?