The Mac version launcher -does- work - I managed to get it running and have been playing CoX on these servers the past couple/few days.
After downloading, when you try to launch the game through Rum/score - in my experience there may be a little delay at times and you need to wait a little, but when the game does load - a small rectangular bar which says 'loading' will show in the middle of your screen first, then a larger window will show up and load the actual CoX login screen in question. Usually it'll be full screen first time around ( but you can adjust settings in game and make it windowed mode etc).
Anyway, I actually ended up needing to download the files of the game twice through Rum. The first time around, some files were messed up - and also I didn't install Xcode when a window popped up requesting to install it in the system during the download process... so second time around I did install Xcode when the prompts it showed up.
So yeah, long story short - the Mac version does work. And in my experience it has been running pretty smoothly.