@Jabi - Just wanted to clarify a couple of things and perhaps give you a few more options for your situation. As previously noted by my good friend Nikita...
I wouldn`t suggest installing VBR on the DC server, it`s better to install it on a dedicated machine. Ideally I would grant the proxy role to a physical machine to offload the backup processing from the Hyper-V host.
Alternatively, you should stand-up a single 2vCPU x 4GB VM in your HV cluster and install Veeam Backup & Replication. If you do not have hardware VSS available with the DotHill Veeam will leverage On-Host Proxy mode to backup your virtual machines. Then within your Veeam console add the Drive on your DC that is to be your Veeam Repository.
In regards to your Domain Controller setup, you have multiple DC's and are leveraging native Active Directory replication, correct? If so, when issues occur you never need to restore an entire DC and would just DC promo another machine into the domain, but then when you're doing backups you can backup the Virtualized DC and leave the physical alone and not have to muck with it.
When issues occur and you do not have access to your Veeam server, if it ever occurs, you can use the Extract utility to get outhttp://helpcenter.veeam.com/backup/80/hyperv/extract_utility.html
Please let us know if you have any other questions.