How does a hardware FCoE Adapter appear to an ESXi host?

Page 39 of the vsphere Storage guide.

D is correct (presented as a vmhba)

http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-50-storage-guide.pdf

Configuring FCoE Adapters

ESXi can use Fibre Channel over Ethernet (FCoE) adapters to access Fibre Channel storage.
The FCoE protocol encapsulates Fibre Channel frames into Ethernet frames. As a result, your host does not
need special Fibre Channel links to connect to Fibre Channel storage, but can use 10Gbit lossless Ethernet to deliver Fibre Channel traffic.
To use FCoE, you need to install FCoE adapters. The adapters that VMware supports generally fall into two
categories, hardware FCoE adapters and software FCoE adapters that use the native FCoE stack in ESXi.

Hardware FCoE Adapters

This category includes completely offloaded specialized Converged Network Adapters (CNAs) that contain
network and Fibre Channel functionalities on the same card.
When such adapter is installed, your host detects and can use both CNA components. In the vSphere Client, the networking component appears as a standard network adapter (vmnic) and the Fibre Channel component
as a FCoE adapter (vmhba). You do not need to configure the hardware FCoE adapter to be able to use it.

Software FCoE Adapters

A software FCoE adapter uses the native FCoE protocol stack in ESXi for the protocol processing. The software FCoE adapter is used with a NIC that offers Data Center Bridging (DCB) and I/O offload capabilities. For
information on NICs supporting software FCoE, see the vSphere Compatibility Guide.
For the software FCoE adapter, you must properly configure networking and then activate the adapter.

NOTE The number of software FCoE adapters you activate corresponds to the number of physical NIC ports.