How to confirm DLC activation -
Look for a monkey symbol on the map, near "Oldtown". That's one of the new missions on offer. There's also two symbols relating to a treasure hunt, along with a new M700 made available at the stores. Find any one of these, and you can confirm whether the DLC has been activated or not.
Also, if you're currently on a mission, the DLC will be activated once the mission's done or abandoned.
80 GB PS3 - CECHL01
Running Rogero 4.30 v1.00 + Multiman 04.19.00