Backup is, probably, one of your enabling services. Meaning, you need this service in order to provide other service(s) to your customer(s). Therefore, it should be part of the Service Catalog, but you will keep this service for internal view only i.e. it will be part of the Technical Service Catalog.
If you sell backup as a service, then it should be part of the customer's Service Catalog i.e. Business Service Catalog.