I haven't seen any documentation for them. I looked for "Telerik" in the source and then found a reference to them in the code... I think I found a reference to them in the code... Anyway; Then I just attempted to use them in a quick test for an attempted integrating into Form and List. Worked pretty well for individual controls, but didn't try to tackle the grid.
I have a dev lic so I don't actually need to use the wrappers, but I'm planning on trying to so I can help with suggestions on how to improve the wrappers [aside from "More please"].
I think following these steps should set you up to use the wrapped controls
*Follow the steps in this blog to get design time support http://www.mitchelsellers.com/blogs/articletype/articleview/articleid/314.aspx
*In Visual Studio [when on the ascx] use the 'Add Tab' on the Toolbox [via right clicking] - [I named mine 'DNN 5.3.1 Web Controls']
*Right click in your new tab and select 'Choose Items'
*Click Browse and go to the DotNetNuke.Web.dll and click the OK's back to the ascx. This should create a bunch of items in the toolbox in your DNN tab
*The ones with not a [gear] icon are the Telerik controls. [The rest are just supporting pieces IIRC]
*Add a reference to your project to the Telerik.UI.DLL - It will compile error if you don't.
From here, you should be able to use the controls as any other ASP control that is in the ToolBox.
For more specifics of the individual controls I suggest the Telerik online documentation at http://www.telerik.com/help/aspnet-aj... [just replace the 'Dnn' with 'Rad' and that's the name of the control - ie DnnTextBox = RadTextBox] I normally have that open when I'm doing dev stuff with Telerik, it's a fantastic help for all the javascript abilities these controls have.
Other than digging it out myself, I haven't seen any docs on how to use them. You might do a solution search on the source project for things like "DNNTextBox" and look for examples of their use. I don't remember many, but I tend to jump in and try things first.
I hope the steps help you, and anyone else looking to start leveraging the Telerik Controls for module development, get started.