That's correct. You would need to license VRanger or other products similarly, however these ones charge per sockets, rather than a host _base_d license (so, if you have REALLY great ESX hosts, you get the privilege of paying more).
At the end of the day, whatever backup solution you decide on has to meet the requirements of your environment.
Another one that may be of interest to look at is VISBU. Check out
www.xtravirt.com for details. It's free, but not sure how well it is supported anymore.