What version of CP are you on? Earlier versions of CP ignores requests and didn't show them in Access Tracker, but in 6.4 you will find them there as long as something is received from the Controller.
Format of the MAC-address sent from the controller doest matter, unless you are specifically testing for something like "client-mac-address-dash".. I believe Clearpass normalizes before using it in the sql check towards endpoint db.
A thing to check..
There is a dropdown on the Cisco WLC (I think under Security/Mac-"something") that defaults to client ip-address. Change that to "Client mac-address".
If you post some screenshots of your configuration on both the WLC and CP we should be able to narrow it down more.
I'm working with the exact same setup these days so if you're unable to get it working I can post some more details with screenshots if needed.