We have had CC3 here since 2002 and no problems, and no tie-in. All we've paid RM for is the server and the licenses. We buy all our hardware elsewhere for a cheaper price. You can run the network the way you want providing you don't interfere with RM's utilities. We have a fully-integrated (linux) proxy and (linux) email server which all work flawlessly with RM. The curriculum and management networks are all integrated with SIMS .net to boot.
Some people have a bad impression of RM for some reason and most can't justify it with CC3; they have changed a lot.