ESXi 5.0 still includes a sky2-driver for Marvell NICs. However, it's still a quite old version (1.20) of the driver.
You can try adding the PCI ID of your device to the file
This works or at least superficially, however the age of the driver is concerning. Hopefully it will work under VM load or in other scenarios.http://www.vm-help.com/forum/viewtopic.php?f=24&t=3501