It seems that the widescreen patch provided results in the minimap becoming stretched, rendering 3/4 of it unusable with the Steam release of Warhammer 40,000: Dawn Of War - Game of the Year Edition, as well as Winter Assault. I don't see any way to fix that, or at the very least do not have the expertise necessary to provide a fix.
I noted this issue is at 1920x1080 resolution.