We are using image-based solution called Veeam Backup and Replication in our environment. So far, so good.
Among other interesting product features, there is one specific VB&R option regarding ISCSI storage that needs to be mentioned – Direct SAN access. Your backup/proxy server can be configured such a way, so that, VM's virtual disks data can be directly retrieved from production storage over ISCSI.
The aforesaid method provides us with completely LAN-free data retrieval mechanis that does not affect our production ESX(i) hosts or our management network.
Thanks.