Pre-requisites for logon account for SharePoint backups and Backup Exec Service Account (BESA) to backup Microsoft Office SharePoint Server (MOSS) 2007 / MOSS 2010.
1. Local Administrator on the WebServer and Database Server.
2. The account should be part Sharepoint Farm Administrators Group. To add the account to the Farm Administrators group please refer the document below.
3. The account should be "Site Collection Administrator" at the top-level site.
4. The account should have "db_owner" role on the Content databases. To provide "db_owner" role on the Sharepoint database refer the document below.
5. For disaster recovery it's recommended to backup the SQL instance, and the system databases along with the SharePoint DBs.