You can find the MAC address for LAN1/eth0 (not the BMC MAC) via the SuperMicro IPMI interface by running the following command:
$ ipmitool -U $IPMI_USER -P $IPMI_PASS -H $IPMI_HOST raw 0x30 0x21 | tail -c 18
The eth0 MAC address will be output in this format:
00 25 90 f0 be ef
A fast search lead me to https://www.supermicro.com/support/faqs/faq.cfm?faq=25788
But right now I can't see the contents of the page.
In the search engine cache it shows this:
There is also: https://www.supermicro.com/support/faqs/faq.cfm?faq=14914