Short the ground isolation of an isolated gate driver
Yes, you can short VEE and VSS to perform coherent measurements on both sides of the IC.

The reinforced isolation barrier between interface and motor side is mainly for safety purposes since VDD could be about 550 V (not with this specific driver but in general electrical drives applications) and international norms require extra low voltages to be galvanically separated from non ELVs to be SELV or PELV if required.