I can’t say anything specific for server 2.0.37, but there have been 10 stable releases since then. The current release, 2.2.11, is designed to work with your client 2.2.6, and the 2.1.1 restore ISO. I’d recommend upgrading the server and restore image to the current stable version to get the improved features and performance.
In any case the restore CD is designed to automatically start as the required Linux user for the restore process. Once running it may ask for the UrBackup admin password, or a UrBackup user name and password if you have assigned multiple UrBackup users. These are the same as you assigned during UrBackup setup and use for the web interface, not Linux passwords.