Okay, another shot with some Software/OpenGL oddity. The vertical FADE Gradient of TNT4 is working in Software Mode but not in OpenGL Mode, seems just like the Fade effect isn't applied!
(also TNT4 MAP02)
No, it isn't. I can look into it for ZDoom's transfer type but right now it is remapping that to a standard 3D light plane and those don't have their own fog.