You can use one, two, or three network interfaces, and the VMware Tunnel virtual appliance requires a separate static IP address for each. Many DMZ implementations use separated networks to secure the different traffic types.
Configure the virtual appliance according to the network design of the DMZ in which it is deployed. Consult your network admin for information regarding your network DMZ.
One network interface is appropriate for (proof of concept) or testing. With one network interface, external, internal, and management traffic is all on the same subnet.
With two network interfaces, external traffic is on one subnet, and internal and management traffic are on another subnet.
With a three network interface, external, internal, and management traffic all has their own subnets.