Modules/Server/orbiter.exe is the actual non-graphics Orbiter executable. Orbiter_ng isn't the Orbiter simulation, but just a wrapper that executes Modules/Server/orbiter.exe. Orbiter_ng is used only to run it with the working path set to Orbiter root directory.
You can achieve the same effect as running orbiter_ng.exe when you create a shortcut to Modules/Server/orbiter.exe and set its "Start in" to the Orbiter root directory.