I hope you don't mind me adding a Canadian contingent to this thread (great idea Rev).
I e-mailed Ontario Parks in January about this as well. Here was their reply.
Thanks for your email – it certainly did cause a great deal of discussion and deliberation here between main office operational staff.
We have to follow policy regulations which are that only 3 tent structures are allowed on the designated campsite at one time. The reason for restricting the site to 3 sleeping structures is so that we can preserve the areas around the campsite. The area around the campsite (mostly where you would find trees and other shrubbery) is considered a buffer area where camping or structures are not allowed.
In other words if the tree that you attach your hammock tent to is in this buffer area, you cannot attach it to that. If you can find a campsite that has trees within the campsite area, you may use these trees to tie your hammock tent to.
Does this make sense – we hope so.