If booking Swan or Dolphin through a third-party, Disney isn't involved at all. Swan and Dolphin are Marriott properties. But, you are correct, you would have to go through the third-party booking agent to make any changes, requests, etc. Unless there is some major discount involved, booking through a third-party can become very cumbersome. It is so much easier to book Swan and Dolphin on the Marriott site or by calling the hotels directly.