I just bought a Workcentre 6515 and I connected it via USB to my windows 7 (64) computer.
It prints fine, but even if I install the Scan USB drivers I can not see the scanner in my scanning utility. The scanning in a USB key plugged directly on the printer works fine.
I don't think it works that way, You might want to check the settings in the SCAN to.. Option in the CWIS -> Properties -> Services. You might need to configure the "Workflow Scanning" or "Scan to Home" options.
CWIS (EWS on this product) doesn't exist when it is hooked up via USB to a PC, there are no network features in that case becaus eit isn't on a LAN.
It did not support scanning via USB cable, only scan to Network, (and it sounds like it isn't on one) and scan to USB stick, which is already working in fact it is still listed that way officially on Xerox.com. But since there is indeed a Scan to USB driver listed for the product, it may have been added after release, in which case you would likely need updated firmware, the latest version is here. I looked at the release notes, it doesn't list it as being a feature added
But my guess is that the driver should not be listed for the product (it was posted in error)