1. Does the Peacekeeper affect my global Submachine Gun stats?
Even though it resides in the Submachine Gun category, the Peacekeeper does not contribute to global Submachine Gun stats. However, the Peacekeeper has its own weapon-specific Challenges, including Peacekeeper Marksman and Peacekeeper Mastery. 

2. If I don't have the Peacekeeper DLC, can I still pick up the weapon and use it in the game?
Yes, if you find the Peacekeeper on the ground, you can use the Peacekeeper in the game even if you have not purchased and downloaded the DLC. However, if you use the Peacekeeper this way—without purchasing the DLC—any stats you gain while using the weapon will not count toward Peacekeeper Challenges.

3. Can I add the Peacekeeper to my Custom Classes?
Anyone can add the Peacekeeper to a Custom Class and use it in-game when playing on the first console that downloaded the DLC. However, when playing on a console that did not download the DLC originally, only users who purchased the DLC can use the Peacekeeper in-game.