I wouldn't consider using a secondary aircraft just as a RF relay. There are many better options out there to maintain comms that don't involve the risk of using yet another complex and prone to failure aircraft. Note CUAV still had comms ground to ground even after the "RF Relay" heli came down, otherwise they'd have not been able to takeoff from the remote landing area.
If you really wanted to run a second aircraft, consider using it only if comms fail, and by using it as a backup aircraft etc, or for doing the initial search and then synchronizing each flight to fit within the time limits and overtime penalties. There are many configuration optimizations that can be used, but overall the less complex and less aircraft, the least exposed to systems failure you are.