I don't think this is correct. 250.6 only says you need to avoid Objectionable Current and there will not be any chance of that because all the loads being discussed are line to line.
Section 250.24 uses the prescriptive language "Shall Not." If forbids the grounding of the neutral on the load side of the service disconnecting Means. The code format changed with the 2020 edition. The first part of the article states what is to be done. The second part prescribes how it will be done. It is the second portion of the article that is used for enforcement. The critical words are shall, shall not... 250.24 Says "A Grounded Conductor
Shall Not... be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article." To say that the article otherwise permits you have to find language in the article which says "May" followed by language describing a situation were "reconnected to ground" would be done.
Search or argue as you will you will not find language that permits the neutral of a generator that is connected to the neutral of the supply conductors on the load side of the service disconnecting means to be bonded to the frame unless that neutral is switched with the phase conductors which would change the generator to a separately derived system. If the neutral is not bonded to the frame of the generator Then the frame must be protected from accidental contact with an energized conductor by the installation of an Equipment Grounding Conductor to provide a low impedance pathway for fault current back to the main bonding jumper so that a fault will cause the generator over current protective device to open and interrupt the fault current before additional damage, electric shock, or electrocution can occur.
The conclusion that brings me to is that the connectors must be capable of connecting 5 conductors, to accommodate the addition of a EGC, to the supplied systems wiring.