I would agree good idea to isolate such devices from the rest of your network.
Either via physical different network or sure vlan switch can isolate them.. Your prob going to to want to adjust the firewall rules on your dmz interface so that the dmz can not talk to your other networks (lan) unless the lan has started the conversation..
Or you could pinhole some things into your other networks. For example if you want to be able to print stuff from these server you might allow that..