The DDS files should be loaded automatically (along with the rest of the artwork) but you won't have the corresponding XML entries so you'll need the <IconTextureAtlas> entries that the scenario adds as well as the <IconAtlas> and <PortraitIndex> entries if the Units/Buildings/Civ/etc definitions
But that's just my problem.
For example, my mod uses one of the static leaderheads from the Viking DLC scenario. I've told my mod that it needs the Viking DLC, then I directly copied the XML entries concerning the IconAtlas, Potrait, IconTexture, etc.. This worked fine, the leaderhead shows up in my game. I didn't need to have the actual art asset in my mod.
So I'm trying to do the same thing for the Goths Civ Icon from the Fall of Rome Scenario. I told my Mod it needs the G&K expansion. Then I copied the XML entries for the IconAtlas, etc. used in the scenario for the icon into my mod's XML files. However, in this case it does not work. The icon doesn't show up in game and instead it looks like when you reference nothing.
So, any ideas how I can use this icon? If I can't just reference it, is there a way to extract it and load it manually?