I'd recommend you to stick with a direct-SAN approach here.Prod:
4 x ESXi Hosts, 1 Cluster
1 x NetApp FAS8020 with SnapMirror/Snap Vault Licenses
1 x FC connected Physical Proxy
Minimal time interval is to start new replication cycle as soon as the previous one has finished.Offsite DR (we want this to be a running replica of Prod with as low of an RPO as we can get):
Yes, you should give it a try as it will reduce the load on your primary storage (actually, backup operations will not touch your primary storage at all thus preserving its performance), all I/O load will go to your secondary array. That will allow you to configure replication with your production storage being the source. Pleas check this article.We don't really use SnapMirror/SnapVault in our current design but maybe we should.
Another option would be to use replica from backup feature as Nikita's suggested.