ESXI 6.0 with a MNPA19-XTR installed in passthrough. I can see it in a windows VM, but not in a FreeNAS vm Why not?

I've been experimenting with FreeNAS and installed it in a VM along with a HBA and a Mellanox MNPA19-XTR (Connectex-2) 10 GB card both in passthrough mode.

I can see the HBA, but not the Mellanox card.  If I don't passthrough I can configure the NIC as a VM device, but I'm not getting good throughput so I want to passthrough.

Also, if I have it in passthrough I can see and use it in a Win 10 VM just fine.

Is there something special about FreeNAS for FreeBSD on which it is built?

Thanks.

Roveer