Update.
Managed to achieve isolating Docker/VMs in the end thanks to the following threads:
Essentially your second/third/forth NIC needs to be set as follows in UnRAID's network settings:
UnRAID Network Settings
Enable bonding: No
Enable bridging: No
IPv4 address assignment: None
UnRAID Docker Settings (Example) - Use your own IP ranges.
Subnet: 10.10.2.0/24
Gateway: 10.10.2.1
DHCP pool: 10.10.2.100/27