As far as I see there is no way in a kendo-treeview to indicate that the current drop position is invalid without overriding clue/hint templates. (Also done in the examples.) It would be very convenient if there would be a method in event arguments of nodeDrag that one could indicate invalid drop targets with. (For that the event should have all the information that the drop event has.)

 Technical side note: The nodeDrag event is fired before the current DropAction of the drag is decided (hence the event does not contain this information). If the event would be fired just before updating the drag hint/drop clue (if there is no reason not to), we could have all the information in the event, and the suggested new method should just set the dropAction to invalid.