On the link posted in one of the posts above there is a video of a hunter pet tanking heroic FoS... if you can pet tank that instance, I'm pretty sure you can pet tank any heroic.
Again Stealthy, I followed BRK and BRR back in the day. Of course all of them are tankable by a hunter pet. But that hunter is going to need to over-gear any kind of heroic content and most likely any badge-reward content that you would get from farming heroics. Also, what's possible and what's regularly doable are two different things.

There's the big question of how are you going to bridge the gear gap between Fresh-80 and tanking heroics. The answer could be arena, but it's not likely to be very successful.

remember when they said that more than one melee wouldn't work when multiboxing? proven false countless times already

I'm about to try and prove another myth to be false as well; 5 hunters doing heroics


Oh, and by the way, the original poster is gonna make this happen sans healer.

At least you had the foresight to see that you'd really need a dedicated healer. (A cool part about this comp is that you actually control the healer and all your tanks are fun little remote controlled pets-- I really liked that about the setup when I ran it).

I haven't looked at PvP hunter teams for a while...but solo hunters are doing well:
That comparison makes no sense. That's like saying that multibox shaman teams will obviously be a bad idea because there aren't a ton of solo Elemental shammies at the top of the ratings. The key difference between a solo hunter and a multibox group is that a solo hunter has complete control of her escape tools and targeting. Things like disengage and trap and feign death and other hunter escape tools are really useful when you can play 1 at a time. They are harder to take advantage of when you have a stack of 4-5 hunters always clumped up.

Hunters are pretty damn useless with someone in your face. It's the tradeoff they have for having the longest range and so many instant abilities usable on-the-move. Post WotLK expansion, there are too many classes that can easily get in your face, stay there, and deal massive AoE. Whirlwind and Fan of Knives will rape you. Unlike shamans, you can't heal and don't get any defensive bonuses of totems. Even without the AoE attacks, anyone who chooses to just infiltrate your stack of hunters can just have their way with you.

So, if you rule out easily doing heroics and PvP in arena (which I think you should), you're left with "maybe this could be a fun BG team". Unfortunately, solo players can take out an individual hunter pretty easily before you can kill them (see above), and with no heals and no rez, you're going to spend a lot of time running your rezzed party member back to you.

This is not me theorycrafting-- I've been there with a real, live team!

If you really, really, really want to beat your head against this wall, my recommendation is to absolutely go Healer + 4xHunters. Priest seems like an obvious choice, but I'd actually recommend a Paladin or Druid-- someone that could potentially have an off-spec as a tank and allow you to tank a boss down if you needed it. (Can taunt off with a pet and buy time for either to self-heal a bit). Druid is a better healer, IMO, since it's not really healing/second that you worry about (pet bonuses are more than enough to make HPS of any healer stellar), it's about coping with burst. You can HoT up a tank target and make sure that there's always a stream of heals coming every second. Pally advantages are the scaling of Kings on both hunters and pets (helps with health pool), beacon healing allowing you to tank-bounce between two pets pretty easily, judgement of light, etc. For farming and BGs, Pally will allow more firepower due to BoMight stacking.

It's just a weird team. It is mediocre or downright bad at almost any aspect of the WoW game. It's a deceptive enough theorycrafting exercise that Vyndree, Myself, and others all tried it for some portion of time. Ellay and I chatted at length about some of the possibilities during BC time, and I actually stuck with mine from 70-80 in hopes that they would work out. (I leveled them BEFORE my shaman team, counting on a time advantage to get quickly geared up in arena). I should have seen the writing on the wall for them during the last patch before WotLK hit, when we had a lot of the new talents and abilities. I figured it would get better.

It didn't.