We use Cisco UCS internally at my company because of its flexibility and sheer awesomeness. On top of the ridiculously cool NIC failover abilities, it lets us do crazy stuff like move entire Hyper-V servers between different physical blades in a matter of minutes.
I noticed today that after installing a new Server 2012 node from iSCSI boot only a single NIC was present on the server. I had added 3 other vNICs via UCS manager, but Windows had only activated the one iSCSI used for the boot process. I checked Device Manager and found all of the Cisco VIC Ethernet Interfaces appeared as if they were missing a driver. When I tried to update the driver Windows reported it was already up to date.
In order to fix this just open up the properties of the VIC in Device Manager, navigate to the Driver tab, and select Uninstall. Repeat for each VIC showing the yellow warning sign. At the end, right-click the Network adapters and choose Scan for hardware changes. The NICs should come right up with a functional driver.