Yes, all tanks do. No, the abilities don't stack. No need for a hunter to provide that debuff at all in a party.

Assuming the tank is not, in fact, a bad. But then you've got bigger problems.

You do realize that the tank may appreciate not having to apply the debuff and concentrate more on other things, right? Along with the other debuffs that other classes can do that pets can also do now, which means they don't have to worry about it if they don't want to do it themselves. There's no rule anywhere that says a tank and a tank only must lower the enemy's attack power, or only a mage can increase magic damage done to a target, etc.

@SillyString

Applying the debuff generates threat, so it's something the tank should be doing. In any case, a 5-man group is likely to be missing a lot of buffs/debuffs. It would be better to bring a pet that can provide something that the other group members can't.

The threat generation is not worthy of a mention unless a mob hasn't been attacked.

This should help with the buffs:

Strength/Agility can be applied by:
-Warriors (in the likely scenario they use Battle Shout)
-DKs
-Shaman (if they use Strength of Earth, no idea what the odds of that happening are)

5% crit can be applied by:
-Feral Druids
-Fury Warriors
-Elemental Shaman
-Subtlety Rogues

Stamina can be applied by:
-Priests
-Warlock Imps
-Warriors (in the unlikely scenario they're not using Battle Shout)

Bloodlust can be applied by:
-Mages
-Shaman

5% stats can be applied by:
-Druids
-Paladins


The order of least likely to have, and thereby best to base your pet on, to most likely to have is probably:
5% crit
Bloodlust
Stamina
Strength/Agility
5% stats

As for debuffs, it looks like they're all rare enough for you to randomly choose a pet. Just don't worry about demoralizing roar if you've got a warrior or druid tanking, because they should take care of it. A couple of other classes can provide the debuff, but it's only AoE for warriors, hunters and druids.

For the full list of buffs: http://www.cannotbetamed.com/2010/10/19/raid-buffs-updated-for-cataclysm/

For the full list of debuffs: http://www.cannotbetamed.com/2010/10/19/raid-debuffs-updated-for-cataclysm/

In addition, the tank needs to get in the habit of providing the debuff himself. You aren't bringing a bear to a raid, you need to have a ferocity pet for the better DPS. True, you could take a carrion bird, but there is likely a better option especially in a 10-man raid.

The tank on the other hand should be providing the 10% physical reduction in raids. That's part of his job and role as a tank. For the most part, it's pretty easy for a tank to do as well. Especially the paladin, it comes naturally through his normal threat moves. I'd say it's much better to bring a buff that isn't provided by your 5-man AND train the tank in what he should be doing anyway.

Skip the bear for 5-mans. Skip the carrion bird too.

@Helston

"A couple of other classes can provide the debuff, but it's only AoE for warriors, hunters and druids."

Not true at all. Death Knights provide the 10% reduction through talented Blood Boil. That's a straight-up AoE move. Paladins apply it through the Vindication talent, which adds the debuff to Crusader Strike and Hammer of the Righteous. Crusader Strike is single target, yes, but HotR the tanking paladin's new AoE move. On a single mob, he uses Crusader Strike. On multiple mobs he uses HotR and Consecration.

All four tank classes apply it through AoE.