At the very least the 'vncviewer' command is not in your path (that is the right command BTW).
On my system vncviewer is in /usr/bin/ (/usr/bin/vncviewer)
execute the following and paste into a reply:
I can't remember if the vncviewer is in the same package as the vncserver. Try installing vncviewer:
If its already installed yum will say "nothing to do".