As an ex Radar fitter on Shacks for many years I have never seen such a facility and cannot recall any interface between ASV21 and the Sonics system. I do posses the ASV21 manual and it doesn't detail any connection or input from the Sonics equipment.
Of course it's entirely possible that it was trialed and never reached service. Not really sure what the point would be, it sounds like it may be getting confused with the TAC display on the Nimrod which displayed many inputs.