Veeam support any CIFS, Windows and Linux Repository with any filesystem/block media that can handle random IO.
Most of the anti NAS recommendations comes from the fact that all kinds of smaller NAS systems (whitelabel server with local disks) causing some headaches at customers more frequently. In most of the configurations a small entry server box with local raid controller work way more reliable at nearly same price range.
I know from my field experience that our biggest customers often use filers like EMC VNXe / Isilon and NetApp. It works well and scales in all kind of dimensions (multiple Petabyte).
Many of our customers use them with multiple GB/s throughput.
At the configuration you need to specify a "Gateway Server" in Veeam. This system need enough ressources and should be reliable and fast connected to the SMB storage.
If the filer has a limited maximum file size (Isilon has 2TB soft / 4TB hard) you need maybe third party software that workaround this (load balancers like dsmISI). I think this is not the case with your Unity.