What you should do is create a new X session using
x11vnc (you have to install that on the server). Login with ssh to the server and run:
x11vnc -display :9
You can now connect to the server using, e.g.,
make sure the numbers in both commands are the same.
The normal display is :0, so that will not show anything. You could explicitly
blank that screen programmatically, but if you just want to prevent others from seeing what you are doing this should be enough.
Please note that you don't have a full desktop, just an X session.
More background info can be found on this site