please help me to understand what is NBAZDB and what is its role in netbackup.
NBAZAD is Authorization Service's Database This is for NBAC.
Looking for MS Windows 2012 info for NBU https://www-secure.symantec.com/connect/blogs/windows-2012-support-netbackup#comment-8889161
Please read through this section of NBU 7.1 Release Notes:
About embedded security services
Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links