DarkRadiant is becoming to be usable for Unvanquished. Models may not be properly scaled.
Download the game file and put it in install/games/ directory before compilation when installing from sources, or in /usr/share/netradiant/games directory otherwise (or the related path specific to your operating system hierarchy).
Set the UnvanquishedAssets repository as engine path in DarkRadiant preferences, set pkg as fs_game and src as fs_game_base.
Download the def file and store it as pkg/def/entities.def in the UnvanquishedAssets repository.
Unvanquished has advanced file layout for maps and resources. Every map resides in separate .dpk.
Filename must obey the rule: map-<mapname>_<mapversion>.dpk, eg. map-station_4.dpk.
Unpacked files you are working with must be put into map-<mapname>_<mapversion>.dpkdir directory,
otherwise game will not find them.
Those are usually stored in a pkg directory, or a src directory when working with asset sources.