Sorry, I have no experience shooting tethered. Here is the list of supported cameras:
http://helpx.adobe.com/lightroom/kb/tethered-camera-support-lightroom-4.html
Uwe Steinmueller
Seems as if LR4.2 improved support for tethering.
Uwe Steinmueller
Try to use my new Canon5DMKIII with LR 4.1 and tethered shooting .... LR rec. my camera but the camera do not work, it just come up with "busy" on the display and trigger
do not function. Help?