Check out http://justinsomnia.org/2007/05/gallery-command-line-uploader/
He’s created a Linux equivalent to the Gallery Remote application that will upload from a Win machine. Not exactly what you are looking for, but it might stimulate a few new ideas about how to get the task done.
I was thinking it would be simple to call the Admin function to import a folder using a CRON job, but it doesn’t look like Gallery or Coppermine (which I prefer) have the ability to do that.