Depending on if you have iSCSI or FC then those are the best options for presentation to Veeam.  If you have VMs on there you can do snapshot integration too which works great.

Yes, I used direct storage access now, though I haven’t setup one specifically on Nimble yet but I have a client I plan on enabling that for down the road. Note that what I’m using is accessing the VMDK’s via ISCSI after the snapshot has been taken of the VM.  There is also deeper integration available where you backup from the the storage snapshot that the array takes of the datastores, but I haven’t been doing that.

With that said, one of my clients ran into an issue recently where I believe Veeam was initiating VM snapshots at the same time roughly that the array was taking storage/volume snapshots and it caused some sort of issue.  I don’t know all of the exact details and the resolution as I’m relatively hand’s-off in that environment, but I know they bounced off of me for ideas.  I’d certainly recommend reading the best practices from both Veeam and Nimble on this integration.  I seem to remember it being something about when presenting the datastores to the Veeam host for direct storage access, making sure that you’re only presenting the datastore and not the datastore+snapshots to the veeam server.  I googled up some best practices and while the below links is clearly very dated (most recent revision is over 7 years ago), I think it may still contain some good information from Nimble on the topic or at least some food for thought.  http://uploads.nimblestorage.com/wp-content/uploads/2015/05/18065708/nimblestorage-tp-veeam-backup-replication.pdf

If I remember correctly, Nimble offers something called Nimble Connection Manager that should provide integration between the Nimble array and your hosts. 

https://infosight.hpe.com/InfoSight/media/cms/active/public/tmg_HPE_Nimble_Storage_Deployment_Considerations_for_VMware_vSphere_6_doc_version_family.whz/xpu1472239915164.html

Yes this software works really well. When placed on the proxies it allows direct storage integration for backups.  It will also work well to add storage for backups on the backup repo server too.

As a FC user “Backup from Storage Snapshot” or “Direct Storage” are worth EVERY penny.

My backups are super fast, and it eliminated the issues I was having when my giant VM’s would stun after a VMware snapshot would grow too much. 

For me it is the best method, but you will need to test for yourself. If you have small VM’s with minimal change, hotadd seems to work very well. There is a few minutes needed to prep the storage snaps on the SAN before the backup begin and afterwards to remove them.  If you have a tiny VM with no change it would most likely be backed up in less time that the snapshot takes take. 

Even on my smaller VM’s I use storage snapshots now to keep things consistent however and have had no issues for a few years.