some engines/exporters will do the "split" internally, but preserve the original normals, so that object appears welded, when it's not. so yes it's possible, but depends on the engine/tools
Infernal Engine had an awesome unwrap feature for Lightmapping. Literally a checkbox that has to be checked and the engine does the rest. No need to setup for a 2nd uv channel and unwrap.
"does that mean Engines you write?" Nooow it makes sense :D Udk, cryengine, Source, Unity, Ogre3d (:poly142:), Hero engine, Wikipedia... ^^ just to contribute. :)
Ok... I guess a better question would be, does postal 2 use the original unreal engine, or the second unreal engine which was used for UT2003, and UT2004.
Another RTX test in Unreal Engine. More stuff like this here: https://polycount.com/discussion/157279/the-wonders-of-technical-art-unreal-engine/p4#latest