I am working with a BSD 64-bit VM and I was fine adding NICs up to 4 in the Web Client(s)
When I needed to add a 5th. NIC, it showed up in the Web Client and/or the vSphere Client (HTML5), but never became available in the VM. I became suspicious and looked at the VMX directly, and sure enough, ethernet0-ethernet3 were there but no reference to ethernet4!
Anyway, I added it manually to the VM using vi and gave it: ethernet4.pciSlotNumber = "1216" - now all is working
BTW: The reason for so many NICs is that I need to bind MAC addresses to IPs for corporate requirement, each NIC= one static MAC address