In order to use the replication destination for testing, you'll need to create a snapshot on the destination side and promote that snapshot. The promoted NFS snapshot will then be accessible by your ESX hosts and used as an additional datastore. Changes made to that writable snapshot will be stored in your Protection Reserve space for the original VMware Storage Resouce.  The ability to promote snaps for NAS-based Storage Resources is only available with Vmware NFS Datastores currently.
I've got a replication destination and I want to mount the .vmdk to a VM as read-only. I have the datastore marked as read-only and the host can see it, but when I edit the settings for the VM to add it, it won't "see" it. What am I missing? Does vSphere make changes to the .vmdk when it is added to a VM?
Can't add .vmdk from replication destination to VM