If the saftey switch is otherwise bonded and the EMT is made up tight with proper fittings, then no grounding bushing is required. If it's between the service and the combiner, then EMT may or may not provide the EGC all the way back to the service. If the switch is on the roof side, then a green wire from the combiner ground bar should bond the switch or something else on that side of things, which could be to a grounding bushing but could be done in another way.
You see a lot of grounding bushings in solar that exceed code requirements because of older (now out of date) requirements for a grounding electrode conductor from the array. It's still good practice in my opinion to bond the EMT on the roof side with a grounding bushing in the combiner, but it's not the only code approved method to accomplish that bonding.
