I had to dig in my memories. It’s been a while that i made games, and even longer that i used DDS file format somewhere. And from what i remember, DDS was never meant to be reloaded into any graphics package. And loading black in Blender/Bforartists could even be intended.
It is a special compressed format for just the graphics card and for useage with game engines. The usual workflow is to create the textures, then compress in DDS. To modify the textures you would need the original textures since DDS is a lossy compression format.
As a workaround you could open the textures in Gimp and save it as png. Then use this png texture to modify what you want to modify in Blender. And then save it as dds again. But as told, it is a lossy file format, you will loose lots of quality.
https://en.wikipedia.org/wiki/DirectDraw_Surface
I have tested the addon meanwhile. And it is one of those unfortunate addon cases that does not work in Bforartists 1. Most probably because of some hardcoded paths towards Blender. Sorry. There is nothing that we could fix. You need to use Blender for that task.