That's an interesting question. I've never noticed handicapped camp sites. But, I wasn't looking.
Did you look up the "Americans with Disabilities Act?" Maybe that will furnish an answer
Or, contact the local municipality/county where the campground is located. Maybe they have an answer.
I think, businesses are required to have handicapped parking available as close as possible to the entrance.
But, a campground may be different.
Are the handicapped sites where you are going close to the showers/toilets? Possibly, that is the requirement for campgrounds.