I agree in principle, I wish it was easier. But after struggling with it for a while, I think it can be done.
I'm hosting VDP on iSCSI zfs volumes. ZFS has snapshots and replication. Replicated appliance is coming on line as I type so I'll report back with results. Here's another DR method utilizing ZFS that doesn't include VDP: http://blog.laspina.ca/ubiquitous/provisioning_disaster_recovery_with_zfs. And here's a blog post showing an example VDP replication technique, though not the one I've used: http://blogs.vmware.com/vsphere/2012/12/recover-replicated-vdp-appliance.html.
If you look into ZFS, OpenIndiana and Napp-it are good searches to start with.