OnOpen scripts do fire in a server scheduled script, quoted from FMI:
FileMaker Server is merely acting as a conduit for the FileMaker Pro clients so that they can open the database remotely, so FileMaker Server itself does NOT run the On Open script when it opens the file. However, when the Script schedule runs, the thread that runs the schedule acts as a FileMaker Pro client, and thus runs the On Open (and On Close) scripts.
basically the thread running the script acts like a virtual filemaker client. So while things are evaluated differently, they are still evaluated.
Mike B is correct. To expand, this is why many developers put a trap in the OnFirstWindowOpen and OnLastWindowClose scripts to circumvent them if they're inappropriate for a server environment:
If [ PatternCount ( Get ( ApplicationVersion ) ; "Server" ) > 0 ]
Thank you everyone. When did this start? I'm assuming in FMS 12. I don't remember this being the case and FMS 5 through 11. Anyways thanks for your help.