Absolutely... Approach used to, I believe, differentiate non-radar... but that is less and less the case nowadays.
Some UK military units use the callsign ZONE on their LARS console, it has nothing to do with whether you are flying in their Military Aerodrome Traffic Zone or not... misnamed, possibly, but the unit may have several radar controllers in the team (e.g. Approach, Departures, Director) so the use of "Radar" is thought by some to be confusing? I am not sure there is any firm callsign protocol (but am sure others will correct me if so?)
Suggest, if there is no callsign published, you call the unit by name (e.g. "Shawbury this is G....") and follow their lead?