To be honest, I start to doubt which storage it was from Dell (but certainly not the newer ones). But still, my point for a support call stand. We used to see a lot of issues with hardware VSS and many work has been done in investigation from our side and updates from the hardware vendors for their firmware to address VSS issues.
Another advice is to read this paper: https://blog.workinghardinit.work/2014/ ... r-channel/
It is written by one of our Veeam Vanguards who is also a Microsoft MVP and has lots of experience in configuring off-host proxies with Hardware VSS and Hyper-V