For sure they are displayed during the installation/setup in the summary.
If you click in DSM on Hardware and expand a CM->IO Ports->iSCSI and select the greyed local port the MGMT Port is marked and you can see a MAC. But iam unsure if this one is also the MGMT and not the optional one for the FlexPort.
If you ping the CM from the same subnet and taking a look into your arp cache you will find the MAC for sure.
Also... some shell access developer from commandline will bring up the addres i think.
If you are physically at the system you can look on the controllers and the MAC address is printed on the sticker in the controller. As Joerg stated you can go into DSM and look it up as well via the steps that were provided.
Please let us know if you have any other questions.