Dukatia exclusively saves data in the postgresql database specified in the configuration.
You can use the native tools of postgresql to take and restore backups.
Taking or restoring backups while Dukatia is running generally shouldn't lead to issues. For a restore I personally would stop the Dukatia backend service though.
If you want to be able to log in you also should save the pepper value from your configuration as that is used to make the hashing of passwords stored in the database more secure.