Well I can absolutely assure you that PART-OPS-SPA-HEMS can be interpreted to allow the technical crewmember to do all of things you need them to do, provided that the role is described in the operations manual and that the training and checking required for the role is also set out in Part D.
Punto I beleive you are conflating regulations. Operating equipment is different to being responsible for primary navigation. Primary Navigation is, under EASA, FAA & CASA, to the best of my knowledge, solely in the hands of a licensed Pilot.
All SAR Rearcrew are Technical crew and just like their HEMS Counterparts they can operate radios, FLIR and "assist" the pilot with navigation.
As such, as is the case on UK SAR Helicopters and MoD Falkland Contract SAR Helicopters, the Technical Crew cannot operate the RADAR and give positive navigation commands to the Pilots. However the latter 2 services operating the AW189 do have a view of the Radar Return on the Technical Crew Mission Computer but, because of the EASA Regs the OE cannot fit the controls of the radar in the Cabin so they only have sight of what the pilots have set up whether it is a good set up or bad.
Some pilots will listen to advice from Technical Crew who have many years of being Radar Operators on Military SAR on how to get the best from the radar - many others will not. Some Technical Crew in the Civilian world do not have that experience.