How do you communicate with a military drone operator over radio?
Some UAVs carry VHF or UHF airband radios to communicate with air traffic control and other aircraft. The voice channel is relayed to and from the remote pilot operator via satellite or another form of datalink. I've heard UAVs taking with Joshua Approach in the Mojave Desert, and one time Joshua called one out to me as traffic and vice versa. I agreed to maintain visual separation, the remote pilot acknowledged and overall it was very similar to dealing with any other aircraft.

I have no idea whether they monitor 121.5 as well as whatever enroute frequency they're using, but it seems plausible that they could.