Per the link (provided by Krazer) to the official forums:
Amending the patch notes: The chests containing commendations and
credits in Outlaw's Den have had their respawn timer increased
dramatically or respawn at a speed correspondent to the amount of
players in Outlaw's Den.
EDIT: Actually these chests have been removed entirely as well as all
resource nodes from Outlaw's Den and Ilum.
This apparently was done because of players exploiting the area to grab more high-end resources than the devs were expecting.
Hopefully, they will fix the previous system's exploits and reintroduce loot to the area. But yes, for now the area is only for your own PvP fun. No in-game loot rewards are available in that area at this time.
As Raven Dreamer pointed out, as of the 1.1 patch released on Jan 18, 2012, the Outlaws' Den (Tatooine) Chests containing Mercenary Commendations are available again.
I have confirmed they do spawn again as of the 1.1 patch. They spawn one at a time. I'm not sure of the exact respawn rate, since there are a handful of easily found spawn locations, but it's around 10 minutes from what I can tell.
They provide a handful of credits and 20 Mercenary Commendations. Probably a random loot item too from time to time.