Nah, it even worked with older compile tools. You could texture everything with a texture (of one solid) and just sky where the light would emit or sky would show.
SKY is just like any of the special textures, except those who need to be 100% same on all sides of the solid (origin, clip).
This is not the case with sky. You can SKY any surface and leave it like that. It wont cause compile errors.
But as i said it will drop light and cause HOM. So use it on sides that wont be seen in normal conditions.
Experiment a bit. The only restriction is it MUST NOT be an entity.
Also check this thread, you might like it:
http://twhl.info/forums.php?thread=18292