is there an advantage to the YUM installer over Synaptic?
There isn't any and its my opinion only. Other members may differ ! I prefer apt-get ( Synaptic ) over yum but CentOS is distro (Server) of my choice.

You can't replace 'yum' with Synaptic in CentOS. Synpatic is a front-end of apt-get and RedHat based distros do not support apt-get package manager.