SQL Server Backup license is server base , One server(computer) per license. and Only DataBK SQL Backup Agent requires a license to run.
SQL Server Backup software includes three programs : DataBK Backup Manager , DataBK SQL Backup Agent , DataBK Storage Server .(For more detail information , please click here.)
DataBK Backup Manager and DataBK Storage Server dose not require license.
DataBK SQL Backup Agent dose backup and restore jobs , and it requires a license to run.
One license for one DataBK SQL Backup Agent per machine , once DataBK SQL Backup Agent is registered , it can back up all SQL instance running on that machine.