If not TCP/IP, what networking stack is in use here?  We are using an NDIS custom packet protocol that filters on MAC address.

And, do you have a common MAC addresse on the physical adapters, and another common MAC address configured for each vNIC in the VMs?

The host NICs have whatever MAC got assigned when the host was created.  The VM NICs have all been set to the same MAC address value.

I am not a network engineer.  I am a software engineer trying to figure this out so please forgive me if I am not clear on on the networking terminology.  

I also want to say ahead of time thanks for even responding, any help will be appreciated at this point.