Is Ground Direction Finding commonly used?
Yes, it is commonly used, especially in large complex airspaces. 

If two VHF direction finders are installed at sufficient distance from each other, they allow the ATC system to triangulate the position of a VHF transmission. This position is then indicated on the air taffic situation display, which helps the air traffic controller to quickly correlate the transmission to the transmitting aircraft, often before the callsign has been transmitted. The controller still has to crosscheck the callsigns, but it helps to reduces workload.

Example of a VHF direction finder