I can not elaborate to much here as I do not have all the answers.
I do not recall any NEC section either requiring or exempting GFCI protection on generators.
Many generators do have GFCI protection which is handy as the NEC does require GFCI for personal using temporary receptacles. But that requirement does not specify how that has to be accomplished.
As far as the NEC I do not see that the construction of a generator is any different than the construction of any appliance most are not covered by the NEC, there are some oddity's like window ACs and now vending machines.
As for UL I do not know, not everything has to be UL listed, electric motors are not UL listed.
Hopefully others can jump in here, I will take a look at my UL book and see if I can find any info.
We have a member here who is an Inspector in NY that wants in use covers on generators, maybe he will jump in here and tell us what he has found.
