With NoMachine for Mac unlimited accounts can indeed access the remote desktop. This is allowed by Apple’s EULA as well. All you need to do is install Enterprise Desktop which supports unlimited connections. Those users will see the same physical desktop.
If I understand correctly what you are asking is for a terminal server for Mac, like we offer for Linux, which allows different users to connect to their own virtual desktop or display which is running in the background. This is not allowed by Apple. If, on the other hand, you’re referring to fast user switching, this is already supported.