I'm hoping it can be registered. I have no reason to think it won't be able to register, because the seller never mentioned anything about the 3G not working, or it being defective in any way, but there's no way to tell for sure until it arrives. Which will hopefully be soon. *fingers crossed*
EDIT: I've contacted the seller for more information, and it looks like it could arrive this Saturday at the earliest, and this Wednesday at the latest. I'll be sure to update everyone on the situation when it arrives.
UPDATE: When I contacted the seller about shipping, they happened to ask me if I knew of a way to de-register the device over the internet, since it had already been shipped. They also said they were leaving their books on the device. This leads me to believe that the Kindle actually belonged to the seller, and that it wasn't stolen.