Hello mwmaif,
well perhaps there's something i'm not aware of, but i'm not sure that giving two NIC the * same * MAC adresse will help them communicate, as by definition a MAC adress is supposed to be unique.
As far as I know, you can only specify a secondary MAC Adress to your adapter (which I think overrides the default MAC adress) :
smitty eadap=> change/show caracteristics of an eth edapter.
Then "yes" in the field "Use the secondary MAC adress", write the new MAC Adress in the dedicated field, "yes" in the field "Apply change to database only", and reboot.
There's a trick in order not to have to reboot the system, but it makes you lose routing table.
regards, and tell me if i'm wrong