What you can do is power down the server, and then remove the Predicted Failure drive once the system is off. Once you remove the drive then boot the server. As you had said, at this point you can assign the spare drive as a Hot Spare, then the rebuild should start. You could move the drive over if you prefer, but it isn't a requirement. If you install Open Manage on the server then you can do monitor and manage the server from the OS, including the raid controller.