RSView ME can use any OPC server; KepServer Enterprise just happens to be included with it. RSLinx Classic (OEM or better) is a very common OPC server to use with RSView ME, but you could use a server from any vendor as long as it complies with the OPC 2.0 Data Access specification.
What I've done with RSEmulate 500 is to define the OPC topic name and use RSLinx Classic as my tag server during development and testing, then when I'm ready to connect to the real hardware I delete the OPC Topic in RSLinx Classic and create a FactoryTalk Shortcut with the exact same name.
That's not an officially sanctioned method, but it has worked for me.