Could I connect the N-tap of nmos_rf to ground?

In TSMC65nm process the nmos_rf is deep nwell structure,the N-tap should connect to high potential to form reverse-biased diode to isolate the internal P-sub.But could I just connect the N-tap to ground since the diode between deep N-well and internal P-sub may not conduct under 0V bias(N-tap and Vpwell connect together to ground)?

You could, but the depletion capacitance will be higher and
have a larger nonlinear component - potentially adding to
distortion / harmonics and drain AC current losses.