Page 39 of the current owners manual for the both EU6500 and the EM5000 generators indicate that there is not a neutral ground bond on these units.
Per the wiring diagram, the ground pin on the outlets is connected to the frame ground of the generators (on both generators). To have grounded electrical service, a bond wire would connect the generator frame to the ground terminal on the transfer switch. The ground system from the breaker / distribution box (usually to a ground rod) then serves as the electrical ground for the generator, as well as the balance of the rest of the system, satisfying NEC requirements.
See Page 39 in both manuals:
EU6500 EM5000"The system ground is not connected to the AC neutral
wire. If the generator is tested with a receptacle tester, it will not show the same ground circuit condition as for a home receptacle."
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