The town of Springdale is adjacent to the West entrance for Zion canyon national Park. I can picture in my mind the North side of that town, some little hills you could climb that would give you good LOS into Zion Canyon.
You actually could some good footage without crossing the park boundary, and that is what I would probably do.
The downside of having the town right there is that there are lots of people around, on both sides of the park boundary, and the first thing you come to upon crossing the boundary is the visitor center, parking lot, and campground.
You could stay North or South of those areas though, so you wouldn't be over people.
However, you don't need to cross the boundary to get done impressive shots, the canyon walls are 1,500 feet above you anyways, so staying further back let's you frame more of the canyon in the shot.
A few years ago a helicopter pilot pulled a stunt of landing in the town of Springdale, picking up a friend, then flying into the park. When he flew back out of the park and dropped his friend off in the town, the rangers got a good look at his tail number. The cops were waiting to arrest him at the St George airport 15 minutes later when he landed. I think one of the charges was something to do with the airspace, so even though the blanket NPS restriction kind if indicates you can fly from outside the park, and cross the boundary, there may be other specific restrictions that would apply (as well as restrictions against harassing wildlife etc that the rangers could hit you with).