The previous way of doing server scripts was to schedule a filemaker file to open. Normally using a .bat file. This filemaker file opens up the filemaker client on the server, runs whatever script is set in the 'On Open' settings and then the client script quit the filemaker pro application. Because this is a client script it can read remote volumes. You should still be able to schedule this in the FMaker server scheduler. Here the scripts are running as client not server scripts, which is the difference.
Alternatively you could schedule a copy of the file to the /Library/FileMaker Server/Data/Documents/ but then that requires 2 schedules to run.