Pardon me if I rant for a moment, but this is something that's been bugging me since Exotic Pets were introduced and this rumor started.

Core hounds are not demons. Core hounds have never been demons. I've heard a lot of whining about letting hunters tame demons, which I agree would be a silly thing, but they AREN'T demons, so it's a moot point. I suspect that this common misconception that they are demons originates from their outlandish appearances and the fact that Void Terror demons (such as the Hound of Culuthas) have similar models to core hounds and use the same animation sets.

However, those demons ARE demons and therefore are not hunter-tameable. (They CAN be enslaved by warlocks. My wife loves doing that; how about making THOSE a permanent pet, Blizz?) Core hounds have always been beasts. One of them is even named "The Beast." I remember joking with my guild years ago - when UBRS seemed like advanced content - that I ought to try to tame The Beast because he was a beast-type mob. I even tried to cast Beast Lore on him once just to be sure I couldn't tame him.

Lore-wise, core hounds are servants of the fire elementals - denizens of the elemental plane, not demonic entities. One could possibly argue they ought to be elementals, in which case the shamans might have a reason to be upset. But there is certainly no lore or mechanic reason they ought to be demons, nor have they ever been - despite the widespread misconceptions and rumors to the contrary, they are and have always been beasts.

As for how hunters find all these new pets, the traditional way is to go around casting Beast Lore on any beast-type mob you're interested in, which will tell you if it is tameable. However, the tireless efforts of other hunters to compile data at sites like the incomparable Petopia (http://petopia.brashendeavors.net/) mean that most hunters just go there to find out what they can tame. In general, Blizz does not announce when mobs are made tameable or untameable unless there are serious bugs with a mob such as was the case with the Death Ravager. (Who could not attack PvP targets or be healed.)