our BSP actually reads a base MAC address from the eeprom in TLV format and then increments them based on the number set in the same eeprom. This is per the ONIE specification. You can use the tlv_eeprom command to inspect and change the configuration.
As per which MAC address overrides which between the .dpc and the eeprom, I would have to look at the code again to see which one is preferred.