Well firstly I would caution you to ensure that they are kept very separate. A common switch or VLAN could panic if it seems to see the same MAC on two ports.
It's been a while since I have done this sort of thing (Solaris 2.6!) where we labelled the NIC with a MAC based on the sub-area-node definition for a VTAM connection to an IBM mainframe. I think we actually set the Token Ring NIC with that and the Ethernet NIC with something else. I think the licence was based on it, so you might need to be careful for that too. I regret that I don't have any Solaris left
The 'It cannot be done!' is a lie, for some architectures at least. Some lesser Operating Systems can't cope though. I think you have it about right though.
Robin