It would seem dangerous to not have the gen frame bonded to neutral so it makes sense that would not be the case.
Isn't the neutral considered switched by the twist lock cord connections at both the gen and the inlet?
A generator that doesn't have the neutral bonded to the frame, will have a 4 wire supply to the premises wiring, the neutral will be bonded to the equipment ground at the service equipment, and will return via the EGC in the 4 wire supply to bond the frame of the generator.
The neutral needs to be switched by the transfer switch for separately derived systems not a cord connector. If somehow the cord connector is the transfer switch then I suppose the neutral could be considered switched but that will not happen.
Separately derived generators are completely isolated other than equipment grounding conductors from the other source and the transfer switch needs to transfer
all current carrying conductors.
A non separately derived generator has the grounded conductor tied to the grounded conductor of the other source at all times but only looks at the transfer method for this determination and not cord and plug connections.