The RadDragAndDrop manager does not exist yet for WPF.
It will be part of the Q2 release, which will be out in July and it will work the same way as it does in Silverlight (same API and almost the same functionality).
For its first version it will rely on UI adorners and therefore it will not support dragging across different application windows (this is the only difference that I can think of).
Hopefully the Q2 release will not be too late for you and you will be able to make use of the drag & drop there.
the Telerik team