Yes. This video purports to show it working on a completely hard-bricked device.
But the XDA thread on USB jigs (
http://forum.xda-developers.com/showthread.php?t=1402286) suggests it only works on softbricks:
"If you soft brick your phone, you can force into download mode using USB jig and reflash new kernel or ROM. As far as i concern, there are few ways to force into download mode, however this is the most simple way to get into it. If USB jig doesn't work, i don't think other method will work either.
"If your phone is hard brick, i don't think this will work."
But further down that thread someone claims it /will/ work on hard bricks... (
http://forum.xda-developers.com/showthread.php?t=1402286&page=22)
So I'm not sure...