JRH,
There are 3 options available to automate firmware updates for HP servers as defined in the following article;
Unfortunately, HP Version Control does not currently support ESX (as you are aware) and neither does HP Smart Update Manager.
Therefore, you the only other option is HP Rapid Deployment Pack which is a licensed product. Within HP RDP, the Upgrade ProLiant ML/DL/BL Firmware job uses LinuxPE, not the production operating system. Therefore you can use it on bare-metal servers. The job upgrades the following hardware: System BIOS, Smart Array, iLO, NIC, QLogic HBA, and local hard drives.
You can also use this tool to automate your ESX server deployment including the hardware configuration.
Hope this helps, Dan.