When you run a plug-in server-side, it will run in the context of the FileMaker Server application. FileMaker Server runs in a non-logged-in state and does not have permissions. You should be aware of this when you use a plug-in : as long as you are targeting files or folders inside the Server Documents folder you should be OK, but outside of that you are likely to get permission errors.
This is an excerpt from Installing Troi Plug-ins as FileMaker Server Plug-Ins
So looks like a no-no.
Try to do this usng just FileMaker Pro and forget about Server. Pro should be able to work with the Folders directly which is what you want to do as Full Access. There is also a chance that what you are trying so hard to script could be handled manually or by another application.
Using Pro and not Server you would need access to the file server of course. I had a client who use FMP to import PDF files on a file server so access is possible. 14 has a new get file/folder path that might help.
The real question is what are you trying to do? One plugin might work while another one won't.
Keep in mind the old adage, if you have a hammer everything looks like a nail.
Any plugin running under FMS runs as the user fmserver. So you don't have permissions to read and write to any folder on the computer.
In order to write to a folder, you need read/write access for fmserver to that folder AND read access to every parent folder all the way up to the root folder.