Apple TV requires you to be logged into a US iTunes account to show the app. 30 day free trial, can pay directly via iTunes account.
Tested it tonight, looks to be exactly the same content as HBO Go, which is every single HBO TV series, and a large # of movies that rotates, and all their sports series.
Works fine using unblock us, I'm going to assume it works fine for every other VPN/geo DNS service too.