I cannot give you a definitive answer.
Proper grounding and bonding in electrical distribution systems can be a complex subject. Neutral to ground bonding is most often only allowed at the main distribution panel using very specific methods. The neutral is not bonded to ground in sub feed panels.
Your Progressive Industries EMS does have some good monitoring features. Using the G-N bonding plug as suggested doesn't really address the no ground condition as much as it satisfies or tricks the Progressive Industries testing design. I can say that bonding the neutral to ground without a proper ground conduction method (water pipe, driven ground rod, grounding mat, etc.) can be dangerous of itself. Bonding to a marginal ground grid can cause some more problems than it addresses. One issue is that bonding the neutral as you describe can set you up for a "Hot Skin" condition.
I would hesitate to give advice as to what is necessary for proper grounding and bonding for a small stand alone generator unit. Connecting a GFI unit at the output can increase the safety of using a portable generator. GFI protection doesn't depend upon ground bonding for the safety it provides so that is what I would rely upon.
Mike Sokol has some good general information here:
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