refer the page 32 of Backup Exec (tm) 2012 Software Compatibility List (SCL)
http://www.symantec.com/business/support/index?page=content&id=TECH175581
Note: A vSphere Standard license is required for BE 2012 to correctly protect the ESXi hosted guest systems.
Note: All free versions of ESXi (4i and 5) require a minimum license from VMware in order to be protected by Backup Exec. This is due to the lack of vStorage API for Data Protection support in the free unlicensed versions of ESXi and is a current limitation of VMware.
so a license is needed