Hi,
Today I was performing an upgrade from ESXi 4.1 to ESXi 5.1 in a bunch of Sun blade servers.
First step was to check if these blade servers and chassis were listed in the HCL and they were.
All of the servers have 2 10GbE NICs beside other HBA and 1GbE. Everything worked fine but the system wasn't able to see the 10GbE NICs even when I added the required VIB to the base ESXi image using PowerCLI.
After that, I tried those very same drivers with version 5.0 and they did work so the drivers are the right ones for that card, but the problem is in the ESXi version or driver version...acceptance level was not the problem as it was correctly set for this particular driver.
I tried everything I could, from using esxcli directly on a freshly installed ESXi 5.1 image (in order to discard any procedure mistake when creating the personalized image) to trying to edit the driver, but without any success.
In the meanwhile I was waiting for the VMware support phone call until it finally arrived with the answer. Even when this server is listed in the HCL and when the driver is available from the 5.1 download page, it is still not functional. The new version, the one that will work with version 5.1 is still being tested by VMware engineers. No time forecast for its availability but at least now I know that I will just have to wait...unless you know other option and want to share it 
There are a couple of tools out there that I have never used but look really cool. The first one is from Andreas Peetz (if you been around this community you sure know who he is)
http://www.v-front.de/p/esxi5-community-packaging-tools.html
And the most recent one is available now from VMware Labs as a Fling from Yong Ding
http://labs.vmware.com/flings/vib-author
But this is something I never tried as these VIBs would be "community supported" which for my customers is not an option.
I will edit this post as soon as I'm aware of a solution for this (hopefully I will remember to update the post! LOL)
Regards,
elgreco81