With my setup I have a Dell PowerEdge 520, Exagrid EX21000 and Dell PowerVault TL4000 running Veeam 8. I have a Nimble CS210X2 and a Dell EQL 6000E, the EQL is going away and we are getting a second Nimble, a CS300, in the next month. My Veeam is hooked up with Direct SAN Access on both the Nimble and EQL and I haven't had any issues. I'm not running Hyper-V, we are a VMWare shop. I use to have Veeam backup over the network, but once I switched it to Direct SAN Access it ran a lot better.
I hope this helps out. Let me know if you have anymore questions.
I don't believe Veeam will do Direct SAN access for Hyper-V like it does with vSphere.
If you're referring to direct connecting your VMs to Volumes on the Nimble with something like in-guest iSCSI - that would restrict Veeam's ability to backup the data on the volume. I'd stick with virtual HDD's protected by Veeam and taking a look at how you can utilize Nimble data protection to improve your RPO/RTO needs. You'd be surprised how easy it is to setup some simple crash consistent protection plans with Nimble to augment your standard Veeam jobs.