Turns out I was reading the wrong FAQ :(
Summary of section 12.1 from the sun-managers faq (not the solaris2 faq)
http://aurora.latech.edu/sunman.html
The Ethernet version 2.0 specification (November 1982) states:
The physical address of each station is set by network
management to a unique value associated with the station,
and distinct from the address of any other station on any
Ethernet. The setting of the station's physical address
by network management allows multiple multiple data link
controllers connected to a single station to respond to
the same physical address.
This doesn't normally constitute a problem because each interface will
typically be on a different subnet. If, for some reason, different
ethernet addresses are required on different interfaces (for example, to
attach two interfaces to the same subnet), a new one may be assigned
using the ifconfig command.
Thanks,
Dave