Does the network need to be restarted after editing /etc/network/interfaces?

You can either restart the nework service or just bring the new/modified interface down and up with a command like: (Note be sure to do this from the console or an out of band management interface)

ifdown ethX (Where X is the ID of your enternet interface) ifup ethX

If you use NetworkManager, then you should not edit /etc/network/interfaces file and the configurations are applied without restart of the "service". If you edit it by hand, then you need to restart the networking configuration for the interface you are changing the config.

And I think that DHCP is not working for alias interfaces (this would be a limitation of the DHCP client).