you're mentioning the keyword there "DB backup"
the maintenance guide refers to a backup of the whole server, including OS and all other stuff you might have in there so when you need to restore you can just re-image the content of the HDD as opposed to reinstall all the SW and then do the DIRT restore
it really depends on the time frame and the urgency you might need to get the system up and running again, but if you think of it this way any company that requires that level of reliability would have a failover system for this and you get enough time to reinstall all on the primary server.
i still recommend DIRT as the best tool to get a backup for unity (just unity and if less than 200 mailboxes) since it saves almost all the config, greetings, etc.
Support Policy for Backup Software
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/support/5xcusupp.html#wp468097
HTH
javalenc
if this helps, please rate
HTH
java
if this helps, please rate