i dont think so, as far as im aware the new lightning connector is still based on usb 2.0 tech.
so it only provides 5 watts/volts w/e
You'd think with a name like lightning it would have been for the thunderbolt port but hey.
I am sure it will. I can charge my iPad 4 with the Lightning cable on the USB 2 port on my Thunderbolt display, and also on the USB 3 port on my 2012 Macbook Air. I see no reason the new iMac would not work also.
It will not charge as fast as the iPad wall charger, but it will charge.