Any portable generator that is hard wired to equipment or devices must be grounded to earth as I understand OSHA. If there are cord and plug connections then no ground rod is required. Is this correct?
I have always questioned why you would even want to ground a truly portable generator (cord loads only). There is a modicum of safety in having the generator ungrounded. With no ground reference, there is no danger from a fault to ground.
There are a lot of small generators that do not bond the neutral, most notably the Honda inverters. This really only becomes an issue if you try to hook one to a 3 wire transfer switch.
I lifted the bond on my 5.5KW genset because my plan is to connect it with my breaker interlock. I already have the pigtail mounted on the side of the house for it. So far we have not had an outage worth filling it with gas. (2 years for me and 3 years for the guy I bought it from) My UPS's carried me through the last one. It was funny sitting there with both PCs running and the TV, satellite etc still going. If the kitchen light had not gone off I might not have even noticed.
OSHA says that any hard wired cord connected supply from the generator has to have a ground rod bonded to the frame of the generator. If you have cord and plug connected only, no ground rod is required.