I'm not sure if they are de facto forbidden, but they might as well be. Stay away, like Gamefreak said. I looked into this for a friend, a few months ago, and as far as I can see, there is no way to set up to deliver a digital product on Amazon anyway, even if it was allowed.
Technically, digital products are OK on Amazon, but only as long as Amazon is selling them themselves, or you're a Kindle author. For anything else, forget it.
Digital Products on Amazon 
