From your answer I understand that you have your own load balancer, that swithes different sitefinity instances on different web servers. In this case - yes you don't need NLB addon.
However, keep in mind that you may experience caching problems, because the cache will be invalidated only on the server where the content is changed. Other servers will not be notified, since they are not connected to each other.
Please contact me again if you need more information.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items