vSphere 5.1 enhanced the software FCoE initiator to enable an ESXi 5.1 host to install to and boot from an FCoE LUN, using the software FCoE initiator (via a NIC) rather than requiring a dedicated FCoE hardware adapter.
Boot from iSCSI, FCoE, and Fibre Channel boot are supported (if booting from NIC then the network adapter must support iBFT)