Veeam Backup & Replication cannot trigger Backup from Storage Snapshots (HP Storage Systems). However, traditional Direct SAN works without issue.
You may find the following entries in the Job.<Job name>.Backup.log or Job.<Job name>.Replica.log:
[timestamp] <01> Info [ViJobSanSource] Can't find datastore LUNs or information in Backup Infrastructure for 'hp' datastore. VM is not SAN mode compatible.
Rescan cannot detect HP LUN even if you added vCenter/ESXi with this LUN to the Veeam console properly: