Since it's powered, it might work. But even if it does... why?
What surprises me is you're using USB at all, which tells me you likely have an older external HD. Does it support Firewire400 or 800? Your new iMac supports both, and both are faster than USB1.0 or USB2.0 and frees up those ports for other uses more common, i.e. digital cameras, game joysticks, flight controllers, and so on. Cosmetically, the Firewire cable also is attached to the back of your iMac, out of sight and less likely to tangle. Just sayin'.
-jim