This depends.
Some CMEs only have one address. In the case of one address, it really doesn't do any good to have a loopback.
Generally loopbacks are meant to provide connectivity to the router even if one of the interfaces go down. If you have one interface, all the IP addresses are down anyways.
If you have multiple, a loopback address can be helpful so that you have one IP address that 'defines' the CME more or less.
Short answer - your call.
