I understand the rule for unused PSG for GTH Column/Quads.
For unused PS_MGTR do I apply similar rule to tie all power supply pins to GND?
Guidelines for PS MGTR pins are laid out in UG583. See table 5-38 "PCB Design Checklist for PS-GTR" on page176.
We also have AR65375, however, I would highly recommend going by table 5-38 in UG583 as it is newer and overrides the AR.