ROXZEE: Why doesn't Gog include the patch? Oh Gog. 20 - 40% of the time always making me go the extra mile on my own to get a game working ;(
kerframil: I suspect it's down to the combination of having to honour the license of any such patch or add-on - if it is even accompanied by a suitable license to begin with - while remaining within the terms of distribution agreed with the game's copyright holders.
In any case, it seems that they decided to ship Unreal Gold and Unreal Tournament with nGlide bundled. Not the fastest solution but certainly a stable and broadly compatible one, given that nGlide is a mature and proven Glide emulator. However, upon first launch, Unreal Tournament does not actually present "3dfx Glide" as an option unless "Show all devices" is selected. This is odd because the GOG version of Unreal Gold launches with 3dfx support by default, if I recall correctly. All of this likely accounts for the number of threads where people are having problems with rendering in UT99, specifically.
It did the trick for me. There was another problem, however - I couldn't switch to any normal screen resolution, the game always froze. What helped, was nglide_config.exe in installation directory, that can change the default resolution.