How Backup Exec is backing up itself?

No you dont need any license to backup Backup Exec.

All the infromation is dumped in bak file which in the Program files\Symatnec\Backup exec\Data directory during the schecduled maintenance.

So all what you need to backup the following directory

1...%installationdir%\Symantec\Backup Exec\Catalogs

because this contains the catalogs to  needed to restores your other data

2. %installationdir%\Symantec\Backup Exec\Data
contains the Backup Exec Database and the job log files - in theory to get back you only really need to backup the BEDB.BAK and bearing in mind that the BEDB.BAK is created (by default) at 4:00am every day as a backup of your Backup Exec database
If you want the job logs as well then the xml files in the data folder need backing up.
You don't need the SQL agent as the BEDB.BAK gives you that info but it is worth checking that the BEDB.BAK is being updated every day (check file dates/times) as you may have a problem if it is not. Change the database Maintenance timings in Tools --> Options in the Backup Exec console if you want to make the database backup happen just before you start your backup job (or start the Backup job at 4:10am).

you may refer the following blog 

https://www-secure.symantec.com/connect/blogs/how-protect-backup-exec-itself