Anything grotesque is covered with black tarps. There will be decorations in scare zones like Pumpkins, Bats, "ghosts" type figures in the tree's in some areas. Nothing you would not see in a Halloween Obsessed Neighborhood house though.
Most of HHN takes place in the buildings outside of the "normal" US park area.
You will be walking through what are the scare zones in the evenings, that's where anything grotesque will be covered, but you'll still see signs of the event. Like a corpse will be covered up, but an alien space ship (just the ship) would not be.