Give the pfsense VM a vNIC and the passthrough NIC, and then see what happens. What you want to verify is:pfSense complains about not finding em0 and em1 and restarts so I can only look at the boot output as it scrolls by though it is pretty fast. FWIW, pfSense runs on the bare metal just fine.
a) Whether the passthrough worked or not
b) Whether the passthrough NIC was recognized by the OS and the drivers loaded correctly
c) Whether pfsense presented the passthrough NICs to the UI.