Hi,
we had to face the same issue (and some more) to integrate the HP EliteDesk 800 G2 in our SCCM 2012 Task Sequence (which was running perfectly on many other PCs like HP Prodesk G1 for instance).
The Silver Bullet is the order in which you load the two USB 3.0 drivers.
USB 3.0 Root Hub driver MUST be loaded before USB 3.0 eXtensible Host Controller driver otherwise no access to the USB (2.0 and 3.0) is possible.
For Info SATA AHCI driver is mandatory to allow the reboot from SCCM agent during OSD deployment step "Setup Windows and Configuration Manager".
Hope it helps !!