When creating a new virtual desktop on the server host, the NoMachine server starts the default desktop as set on the system. In this way,  the server is able to launch whichever desktop the administrator would like to use.

NoMachine supports most common desktop environments, e.g GNOME, KDE and many more. 

However, due to the great variety of desktop environments available for Linux hosts, it can be that a certain desktop does not run out-of-the-box. In this case, NoMachine developers will try to do their best to provide a fix so that users can run their preferred DE.

The NoMachine set-up v. 5 or later is able to detect automatically GNOME, gnome-classic, gnome-fallback, Unity, Pantheon, KDE and LXDE but you can configure NoMachine to run also a desktop not detected automatically or desktops different from the default one set on the system.

To do that, edit the node.cfg file (namely /usr/NX/etc/node.cfg),  ensure that the DefaultDesktopCommand key is uncommented and set there a proper command for launching the desktop environment of your choice.

Ref. http://www.nomachine.com/AR04K00667