TigerVNC + SSH without a VNC Password?

From the TigerVNC manual. man Xvnc

-SecurityTypes sec-types
    Specify  which  security  schemes to use separated by commas.  At present only "None" and "VncAuth" are supported.  The default is "VncAuth" - note that if you want a server which does not require a password, you must set this parameter to "None".

So -SecurityTypes None on the server is the correct answer to your question. I have tested it, and it does work.

Running vncserver -SecurityTypes None will let users connect to the VNC session without a password even if a password is setup.