You can find the list of the simple HTML elements as well as the standard ASP controls which can be decorated by the RadFormDecorator in Integration With Standard Controls
help article. You may also find useful the effect of RadFormDecorator on RadControls in Integration With RadControls
HTML elements like divs and tables, however, do not get in the decoration scope of the RadFormDecorator control. What I can suggest, however, is to consider that RadFormDecorator applies its wrapper classes to the HTML elements and use them for a CSS cascade to style any elements that cannot be decorated by RadFormDecorator. By using the RadForm_SkinName to cascade, you will ensure to apply the styles you like to the desired element you want.
I have created a short VS example that illustrates such approach on decorating Table element with Forest and Sunset Skins. Once you have created the styles for the skins and set the classes to the elements, you can use the ShowChooser property of the RadSkinManager, in order to change the skins of the styled elements.
You can find the VS example as well as a short video that demonstrates this in the attached archive.
Explore the entire set of ASP.NET AJAX controls we offer here
and browse the myriad online demos
to learn more about the components and the features they incorporate.