The datasheet section 7.3.13 specifically addresses how to disable the chip by pulling down SS or Vsense. Years ago when I used the UCC28070, I pulled down SS to disable it. It was for a 20kW design, so we used LEM current sensors inline with the boost inductors instead of CTs on the FET drains (and thus we did not make use of the UCC28070's current ramp synthesizer feature).
Overriding the error amplifier outputs is an effective way of throttling the output power (for example, overriding VAO gives you direct control of output power), but I don't think it will totally disable the GDx outputs. You may still see narrow pulses coming out.