Please, review the article on data-binding the RadRotator control - http://www.telerik.com/help/aspnet-ajax/rotator-data-binding.html. You can provide any IEnumerable type as a DataSource.
As far as how to get the images from Sharepoint is outside the scope of the Telerik ASP.NET AJAX controls, therefore I should advice you to contact the Sharepoint support or check online resources on the topic.
Hope this helps.
the Telerik team