Over in the Dark Universe reviews thread someone who has been to the park reports the sightline of the Helios is bad from the coaster side of the land. I'm sure tree growth will help a lot of this as having tall trees right next you will block the view of something -- even something tall -- farther away. But I suspect the worst problem is where walkways align with the direction of the hotel so there's nothing between you and the visual intrusion...ever.
For that reason, I suspect the walkway leading from Darkmoor back to the coaster -- highlighted in red in these images, with Helios in blue -- is where the sightline will remain the worst long after trees have grown in around the coaster and queue.
This stretch, which also sub-optimally runs along a backstage building, would be a great place to put a spooky Old World covered bridge, as in these examples. Not only would this "tunnel" block views of the Helios along this stretch but it would serve as a transition from the village of Darkmoor to "the country" where the encampment of the Guild of Mystics is.