I have an ESXi (5.5) environment. There are two redundant domain controller(Active Directory, WINS, DNS, DHCP). What kind of possibility do I have to backup these domain controller without stopping any services? DNS is AD integrated. Does it make sense to Backup all these roles? Thank you in advanced!
There are many ways you can do backups.
"Everything you need to know" about Active Directory backups: http://technet.microsoft.com/en-us/library/bb727048.aspx
A few points about VMware snapshots and backups:
In regards to should you back them up: I'm guessing they are important and that being able to restore them with confidence in a timely manor is also important. Even with redundant DCs, your recovery in event of needing a full restore will go much smoother if you can recover both of them.
In general, restoring AD, SQL et al is a topic of entire book chapters.