as far as I know kot-in-action never touched the engine code and they did a game, an expansion, and in the next months (hopefully) , another game!
Content pipeline in DarkPlaces engine is pretty straightforward: IQM to make character models, OBJ/ASE to props models. All of these directly output from Blender. No converter, no inbetween steps. Shaders to make things look better and you're done!
Only things I miss from UDK is a Kismet-like application (even for cut scene acting), a decent Physics System (ODE?! come ON...), a REAL menu system and particle editor.
But don't worry, just the time to learn C programming, and in maximum 40 years and I'll update DP myself!!
