Remember that the land that the Four Seasons and Golden Oak sit on are no longer "controlled" by Reedy Creek, they were de-annexed before they started building. However, the area is still listed on the District's land maps, as is the Celebration land, since I believe they are the ones providing utility and emergency services to the Four Seasons and Golden Oak property.
As to if the District has a design board or visual design guidelines, I don't believe they do (remember, Disney has many different themes spread throughout property), as I've never seen or heard of one. But, as I mentioned above, I don't think it would matter if they did, as the land is no longer "within" the District.