I actually never understood the parallel neutral violation in cases like this. Where is the hazard? I think in an emergency situation where connections may be shaky, I would rather have a redundant neutral/ground path than have 2 separate ones.
Just the usual parallel path neutral issues like if you had a meter/main service out at a pole then a 4-wire feed to a house panel that had the transfer interlock and the generator was always plugged in.
Then say the neutral went bad in that feeder. Possibly elevated voltage on the generator frame or neutral current flowing thru the generator, to the equipment ground back to the intact neutral in the meter /main.
