Wait, either you have two running core switches in production or a single switch that you need do a factory reset? If you have two running, working switches and can't access them via serial, the serial cable is broken.
The MLXe has slots for two management boards, active and standby. Are two management boards build into yours? What I said is, if the MLXe is not booting upright, you could remove one of the management boards and re-try to access the plugged in via serial.
Yes, the management port is pure ethernet, and you can attach it to a network. With some luck, it got DHCP enabled.