If I try to drag&drop a JPG (or other Graphic file) from Nautilus via the Unity Dash into Scribus, the Dash symbol’s are "grayed" and only some App's are usable but not Scribus.
How can I make this symbol usable for Drag and Drop?
First, download and install Scribus 1.5.0. A PPA is available from here. With it now installed, open Scribus and being a new document. In the Extras menu option click on Picture Browser: