You'd be better off using the GroupText Macro.

--
Maintainer of an unofficial WebGUI FAQ Please contribute questions or answers!
_{When asking questions on this forum, please indicate (at least) which version of WebGUI you are using. Optional, but sometimes helpful, are your Operating System name and version, PERL version, and Apache version. The little icons next to my picture indicate my IM status. Yes, you are welcome to IM me. I am not an employee of Plain Black. My offers of assistance are subject to the general disclaimer of this discussion board that my answer may be completely wrong. Have a great day!}
U2U crythias on #webgui on irc.freenode.net

Actually, the snippet's being processed as a template with session template vars only, as listed in WebGUI::Asset::Template::Parser::addSessionVars.  isVisitor isn't one of them.

The comment in that function says further use of session template vars is deprecated, however.  Hrm. 

This is not a bug.

The documentation for the Snippet says that if you enable Process as a Template that you only get access to the session variables. 

If you want the containing Asset to process your snippet as a template, you should not request that the Snippet itself be processed as a template.