Don't you think a hayride seems... impractical?
It seems more small town USA than huge theme park event.
It works when you have 40 civilized people rather than 30,000 drunk and unruly strangers.
I wouldn't want to sit in hay covered in puke after some drunk barfed all over it.
I know hayrides are a part of fall and Halloween but they are not really coporate america scare.
It's more charming and quaint than scary.
Besides it would require space and employees already working the event... Which there really isn't any to spare.
What I would expect with that sort of ambience would be more like a theme in a house.
Barns, hay, pumpkins, wagons... Heck I wouldn't even mind a "Hometwon horror" type house where something befalls a small town.
But everything has to flow so they can get people in and out. That is the goal with an event this size.
I can't imagine the complications a hayride would cause to flow control.