For the Chameleon trunk, detection for different OS X versions for the GUI was added to the trunk in rev1738
and detection for Mountain Lion for use in the GUI was added in rev1990
I don't use the Chameleon branch Chimera, but providing the branch is kept in sync with the Chameleon trunk then it should support detection of different flavours of OS X in it's GUI. And to confirm, I've just looked at the gui.c
file in the Chimera release source folder I can see the features have not been included so unfortunately users of the Chimera branch don't get to benefit from this nice feature.
If you want to try out the latest version of the Chameleon trunk and it's themes then I recommend you create yourself a bootable USB memory stick for testing purposes to make sure everything works for your system - this way you still have your current setup intact on your HDD. Then if all is good and you want to use it full time you can look at replacing your boot file on your HDD from your installation of the Chimera branch with the boot file from Chameleon's trunk. There are plenty of guides out there to show you how - and you can do it yourself manually using the Terminal or use maybe Conti's excellent myhack, or the Chameleon package installer (though I haven't used that for a while myself).
I look forward to hearing that maybe you've tried it...