When we were at Yellowstone NP 2 years ago there were more than "just a few" trailers that were being turned away from campground registration because of trailer length. People were reserving "any available campsite" and arriving with a rig that was longer than the site could accommodate. The registration desk at Yellowstone was telling them that they wouldn't fit and refusing to allow them to register or park on the site even though they had reservations for the site.
So, without knowing that you'll fit "within the site boundaries" you may find that the campground workers will look the other way, then again, you may find that you're turned away and may not get a refund. It's good that you're asking the question, but I'd suspect that you'll get better information by actually calling the campground and discussing the situation with the campground supervisor.
I don't think you'll get much traction at the campground by saying, "But someone on Keystone RV Forum said...."