The answer: Yes, we can, but you need permissions.
When you login to a FileMaker Server and you mount a network drive, this drive is only accessible for the current user (your admin account). It is not available to other accounts on the server including the FMServer or SYSTEM account the FileMaker Server uses. That is a common problem for us here.
One solution is to mount the volume for all users on the local machine. And to provide permissions for anyone to write to a specific folder.
Another solution is maybe more elegant:
You can use Files.Mount to mount the shared folder yourself to a local drive letter. Than you copy files there and later you unmount it with Files.Unmount. This way you only mount when needed and you have full control over what credentials are used.
To copy files or folders you can simply use Files.CopyFile function.