There doesn't seem to be much information available from VCO to provide DHCP information. I am not versed in using APIs, but you may to check and see if there is some additional information you can pull from VCO using APIs, or even that List Client info, without needing to log into VCO, navigate to Test & Troubleshooting, run the List Client task, and wait for output.
You would probably be better off setting up your own DHCP server (there are plenty of free options out there using Linux), and configure the Edge 610s for DHCP Relay.
Regarding MAC address filtering...if you look at the Firewall options in the Velo Edge, you can define ACLs using MAC address as the identifying criteria, and then Allow or Deny. That should work for you. I just tested it, adding the MAC address of a computer that can connect to the Velo Edge, and setting the option to Deny, and it cannot connect to the network.