Aaah, thank you! Though using Fedora since v16 I wasn't familiar with systemd yet, just because there was no need to deal with it until now :-)
So just in case anybody running into the same problem: If you want to run UT 2004 on Fedora 18 and experience there is no sound, it's because the snd-pcm-oss module is not loaded. So instead of doing
# modprobe snd-pcm-oss
each time before you want to play, you can create a file named like e.g. "ut2004.conf" in /etc/modules-load.d and put in the modules you want to be loaded at boot time, in this case "snd-pcm-oss" (without the quotes).