I certainly don't want to start an arguement here, especially since I'm the newby.
But, I was at the RV show in Austin about a month ago buying my Sierra 355QBQ, and there was a FR factory rep there also. I asked him this very question since it is a hot topic, explaining that I have a 4-bike rack. He said FR has no problem at all mounting a 4-bike rack to the bumper, as long as the coach is a model with the heavier bumper. Some of them have a bumper like a soda can, but mine is quite heavy.
IMHO, as long as you make sure it is tight so not to wiggle around, and it's the type that spreads the load out across a bigger section of the bumper, you're ok.
I have this rack and it's worked for me for over two years.