Your best option with Cisco UCS, is to download the Cisco specific ISO from VMware’s website. Same place you normally download ESXi, but then go to Drivers & Tools tab and expand OEM Customized Installer CDs. There is one for Cisco for 5.1.0, but not for 5.1.0U1 yet.
Otherwise, you would need to download the VMware specific drivers for that server model from Cisco’s site, and inject the vib’s into the image manually and create a new ISO.
Chris DePetro
VCP, OCP, MCSE