Backup running backs don't have to have good years based on the injury of a starter. Some backups have good years regardless.
It's also hard to define what a good year for a backup is. Is starting a good year? Or is 500 yards from scrimmage and a couple touchdowns good? The answer is, it's a little bit of both. Some of these guys I think will start and possibly have 1,000 yard-seasons.
Others will have a great role on their team, and create situations that will help their team win.