We have same situation, game was completely sealed, Metal Box Hardened Edition. We have not been able to redeem the DLC codes at all, I think we were lucky to get the via web-PC the music from the coin... nothing else! We have a ticket, we sent feedback, Activision has not helped...
By the way, we live in Finland, so seems to me from all comments that Activision published some codes that certainly DO NOT work and they are not facing the people due to, perhaps, percentage of those broken codes... If I understand something about DLCs, those are generated by a tool like SW licenses are, they may have had a BUG in the code and we are just suffering from it What else?
HEY GUYS ! FINALLY MANAGED TO MAKE IT WORK ! ! !
I found the Auto Patch Download that happened on Nov.14 (The second which is pushed by Activision) did not show Version number, it said INSTALL but was not like the first patch in terms of information of the package, it did not either allow to reinstall or anything else so....
I deleted it, restarted PS3, got into the game (did nothing), got out of the game, tried old way to redeem codes (Via Account info --> NOT in PSN STORE!) and Voilá ! ! ! It went in and started working!
Now my next step is to try to find out how to get the second patch to the game back again... I hope it comes when restarting the system and game again.
SOLUTION: The codes are region protected. My friend has two accounts 1 Asian and the other American. The disk he bought was American and when he entered the code from the Asian PS Store the error message came but when I told him to enter it from the US account, presto it worked. Please check what you region is and what your game's region is. This whole mess is just because Activion and Treyarch protected the codes and look at them, they don't have a clue what is causing this, they will give away more codes to people and may get scammed too