For some reason the peacekeeper does not count toward this. Is this a known issue? I do not use smgs to much but just decided to try to unlock this Calling card
I noticed the same thing. I tweeted Dan (@OneOfSwords) and he replied back with "Probably because it's additional content and not part of the core game - it's a bonus weapon".
He did not say anything about them fixing it or adding it. Like you, I was hoping to complete the "SMG Kills" challenge because I enjoy using the Peacekeeper.
I will update if I hear anything else, I also tweeted the same question to Treyarch, Call of Duty, and David Vonderharr.
I updated my post in the Technical Support forum but thought I would update here as well: