You can only get the dining plan if you are staying at a Disney owned/operated resort. The Swan and Dolphin are on Disney property, but they are not owned or operated by Disney. They are Starwood Hotels. The Swan is one of their Westin and the Dolphin is one of their Sheraton hotels. While they have some of the perks of Disney owned resorts (e.g. EMH), there are other aspects they do not (e.g. no dining plan, no Magical Express).