The Richfaces Gmap component is a wrapper for the standard Google Map widgets. You can use the whole set of functionality Google Map API provides for you. See Google Maps API Version 2 Documentation for Google Map API features.

Gmap has built-in Ajax capability. You do not need to uptade the component using reRender to see the changes. RichFaces Gmap component is good together with Ajax4jsf jsFunction component that allows to invoke the server side data and convert it into a JSON format.