Whatever user is running the Texis Monitor, runs Vortex scheduled scripts too. because the Texis Monitor starts them.
Under Unix, the user running Texis Monitor should be the user you specified at install (because monitor is chown'd and setuid to it, and texis is a symlink to monitor).
Under Windows, the user is usually whatever user runs Windows services, if the monitor was started as a service. If starting as a service failed, it may be whatever user ran Vortex/texis/etc. which started the monitor -- which may be the anonymous user if that Vortex was run via CGI from IIS.