Sadly the camp host gets a lot of blame but has little real power in many campgrounds, His/Her job is mostly registration and perhaps some janitorial work. They can not enforce rules, but they can call the management to have them enforced.. Again, this is in MANY not all campgrounds.
So I'm not going to comment on the camp host save to say that the host should have told the 2nd Vet that the site was already taken by a disabled Vet.
I will comment on how you handeled it (going to Home Depot for the night)
If you have such an option, it's always better than getting in an argument. You already did your argument service (Thank you very much). and as you know the fight avoided is always better than the one you fight. Wish more people understood that.