Recently my son couldn't use UK PP in XBOX site to change his gamertag (yes they charge even nickname changes btw), it is rejected by PP region. VPN was on, it doesn't seem like an IP issue. That's why i'm checking US services.
Why not sign-up first on the Hulu website with VPN (maybe you can use a prepaid card for this if this isn't blocked) and sign-in with your xBox afterwards? That's what I would try at least.
Otherwise just pirate the content as that might be easier.