I doubt there would be an easy way for them to have the heat tape and not have it plugged into a nearby electrical box and I seriously doubt they would spend the money to have both the metered box and an unmetered box at every site, just to hook up the heat tape. In my opinion, it is clearly just the cost of having water available at your site.
As for the rate being much higher than the residential rate, commercial rates (which is what an RV park is likely to be charged) are often much higher than residential rates. It's politics. The State public utility commission doesn't generate nearly as many irate voters by approving requests by utility companies for higher rates on businesses than they do by allowing rates to rise on John Q. Public.
