Capturing over USB is supported now.
Live View over USB is forthcoming.
This is the case for both the IQ1 and IQ2.
So for now you are limited to live view on the digital back itself, or on a computer via firewire or thunderbolt (using the firewire adapter).
Does live view on the back work when using USB3 tethering?
The D800 does not do live view on the back when tethered.... Rather a pain, but at least I can have HDMI live view