ProFTPd required?

If I plan to only allow vmin users access to sites via sftp, Is there any reason to run ProFTPd?

sftp is a OpenSSHd subsystem, you do not need proftp

Agreed – SSH is nice and, well, secure – and you’re welcome to disable ProFTP in favor of that.

You can disable FTP in Virtualmin by going into System Settings -> Features and Plugins, and disabling “ProFTPd virtual FTP”.