Epic Games VP Mark Rein has posted an update on porting UT3 mods to the PlayStation 3:
We're very close to releasing an update to the Unreal Engine 3 editor, that comes with the PC version of UT3, that will allow UT3 mod-makers to cook their mods into the required PS3 format. We've been doing some internal testing and we're hoping to expand to a wider group tomorrow or Friday. If all goes well then we should see the update released next week which is what I expect will happen. Obviously the process works, as we put out a few mods before Christmas and people seem to be playing them, but it is the update to the editor that we're testing.
If all goes well, using the tool will be as easy as clicking an "Export to PS3" menu item!