It really doesn't matter in public parks because there is usually way more space between neighbors and also vegetation. We volunteered in one national park and the party wanted to pull into the site. To do this and to get angled into the site correctly, he had to drive the wrong way on the one-way street. He was quickly told to back into the space.
In private RV parks where sites are close together, I don't think this would or should be allowed. Side-by-side pull-through sites are bad enough. This is why we don't do private parks. We like our space and vegetation.