Trying to accomplish something similar with a Nimble SAN. Specifically want to use an offhost proxy server to grab the VHDs directly off the Nimble volumes that the HyperV server uses.
Installed Nimble's hardware VSS provider on the offhost proxy server (happens to be the Veeam mgmt server as well) and used "vssadmin list providers" to confirm I see it.
Made iSCSI connection from Veeam server to the volume that holds the guest VHDs. Under the offhost proxy settings for Connected Volumes, I can see this volume on my HyperV server. However when I run a job it fails in 23 seconds with
Unable to allocate processing resources. Error: No offhost Hyper-V backup proxies are avaliable
Do I need to install the hardware VSS provider on my HyperV server too? Do I need to mount the volume as a drive on the offhost proxy server?