From my reading, this is neither U.S. military or U.S. private contractor. They may be looking for some language skills and urban policing expertise. But I don’t see a lot of NYPD signing up for this.
An executive stroke of the pen is probably required to make a hitch part of official US mil time, which might trigger the "no department refusal" thing. GW gonna go for something like that? A couple years ago I woulda said 'no way.' Now....? And the new guy at the top of the UN is someone a tad more conservative than Kofi.....to maintain good relations, the USGOV might go for it??
I do know that the reservist cops considered UN duty a really good gig. In fact, I wouldn't be at all surprised is pressure were to be applied from the police union(s) to make it happen.