Uhm , you have a bit of confusion...
VNX(e) is supported as a primary storage, the one mounted on vSphere where you run the different virtual machines.
For backup storage, Veeam supports windows and linux servers, SMB share and deduplication appliances. You can configure an SMB share on the Synology and send the Veeam backup to this share, without any need to mount it in the ESXi servers.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1