The DRS Guide lists three software options that are officially supported and tested by Cisco: OpenSSH, Cygwin, Titan. If Win32-OpenSSH is really OpenSSH you can argue that you're using a supported option; however, the Github project clearly states that v0.0.9.0 is "non-production ready" which undermines that argument. Cygwin is traditionally how you ran OpenSSH on Windows. The problem is that if you have a issue with Win32-OpenSSH you'll have to debate it with Cisco TAC. In all likelihood, they will take the position that you're not using the exact same OpenSSH on GNU/Linux that the BU tested. They will likely ask you to reproduce the issue with one of their sanctioned options.
Trying Win32-OpenSSH and seeing your your backups fail isn't so bad since you would know of the failure and can decide whether to debate it with TAC or take a different path. However, I have personally seen a customer be burned by venturing off the sanctioned list of options with no indication of a problem until they needed to do a restore. That customer was using a different commercial Windows SFTP server - not FreeFTPd - and DRS showed the backups were completing successfully; however, the backup file was always corrupted and weren't actually useable. DRS couldn't read the file when we attempted to perform a restore. Ever since that day I warn customers: deviate from the supported options at your own peril. IMO, it's just not worth the risk. If you really want to run on Windows and have a clean GUI, go buy Titan. If you're willing to use a CLI and GNU/Linux-style configuration files, use Cygwin; otherwise, spin up a GNU/Linux server.
