Just had another look at the naturehills site, loads of trees and shrubs that are hardy there, some notable/useful ones:

Chinkapin Oak
White Oak
American Hornbeam
Linden
Kentucky Coffee Tree
Chinese Chestnut
Chestnut Oak
Lilac
River Birch (probably others too)
Star Magnolia (probably others too)
Crabapple

I reckon there must be plenty of honeysuckles, hawthorns, elders, maples, pines, firs etc that are hardy there too.