One hunter in a mixed group would work quite well, imo.

You have one serious drawback which all melee toons share.
Follow breaks when a toon enters melee combat.
Unfortunately for a hunter, you automatically switch to melee from range, when your target gets close enough.
Still, you can re-enable follow, or just be careful and park the hunter back with the caster types.

Aside from heroics, the pet can off-tank fairly reliably, especially if you're BM spec.
A hunter is fairly easy to macro their dps to a one button mashing.
If you have three dps buttons between your dps, you could put this hunter macro on all three keybinds.

Hunters bring strong single target dps.
There's the pet.
Some of the aspects are group usable including Nature Resistance and the Pack Travel.
Traps can be used to snare or crowd control.
Misdirect can help establish immediate threat on a boss or an add.

As long as you're aware of the follow breaking on melee, a hunter is a strong addition to a team.
The more classes you add the stronger and more diverse a team is, but the more it takes to play the team to its potential.