I recently jazzed UT2004 up with custom maps/models/skins, then went to test it in another user account to make sure the default configuration still works normally. The result wasn't what I'd expected:
Further checking produces this result in all user accounts except my normal account - where UT still runs just fine. I can't recall ever launching UT2004 from any of the other accounts before.
I'm thinking this is a 10.4.3 problem, where it does a check on applications never run before in that account. It may be tripping up on UT2004 because it uses a symlink in the /Contents/MacOS/ folder, with the binary executable file actually in the app's /System/ folder. This configuration is used in UT2003 also and didn't cause any problems before 10.4.3 started doing architecture checks.
Anyway, could someone with 10.4.3 and UT2004 jump to another account and see if UT2004 is accessible? You'd need an account in which UT2004 has never been run before. If need be, create a new account to check, and delete the extra account afterwards.
It's possible my Tiger install is a bit weird, or my UT2004 install. But it's also possible I've found a bug in 10.4.3.