WebHelp is really for running from a server so it is best suited to web apps.
CHMs are now really for local installation and thus suited to locally installed applications.
Both can be run locally or from a server but there are issues when not run as above.
I believe Visual FoxPro only generates apps for client installation so CHMs would be the way to go.
See www.grainge.org for RoboHelp and Authoring tips
But it is possible, right? I think that the application is both premise and hosted but I'm checking on that.