Well, originally I thought it would be fine to hold a 4 bike rack. We have used it that way for the past couple of months without any issues. However, last week we were pulling in to our campground in Medora, ND (on our way to Glacier Park, MT) and the bumper gave way. The welds broke almost halfway from the bumper to the top of the frame. The bumper did not fall off, but we could not keep the bikes on it any longer. We ended up hauling them in the back of the truck and a couple in the back room of the fiver.
The 4 bikes were NOT that heavy- they were all "Specialized" lightweight bikes. I can't imagine they weighed more than 150 pounds total. We saw several other SOB fivers with the exact same set up in Glacier. Talked to a couple of them and none have had any problems. I am a little disappointed to say the least. Just tried contacting my dealer to see what can be done.
I would guess a generator is going to put the same kind or even more strain on it. Not recommended without some extra support being installed.