Realistically, OUI space is pretty large for each L2 domain... Once it
hits an L3 domain, you can repeat OUIs all you want... Pick some prefix
set of bits that include "locally assigned" that is unique to your
organization and you will operationally be fine. Or the last 8 bits of
your host server's base MAC (hardware) address -- plenty of entropy there.
Even when two or 10 organizations merge, unless you are merging them
into the same tributary L3 domain, its not a problem...
And if it is a problem for more than 1 or 2 virtual machines, I'm sure
your organization is big enough to split that into another
domain/vlan/what have you.
Yes, its a nice idea to have a BCP that works without conflicts, but
I don't see how this is legitimately going to affect anyone more than
theoretically... unless someone's device is really bad at generating
OUIs; all of this based on the cheap prevalence of L3 devices at the edge.
Deepak