I have a customer with some SQL servers on a DMZ, that they need to restore databases to, and we looked at the documentation for which ports to open.
This is the documentation for Veeam B&R 9.0, and we found the ports and it worked fine, until we had to restore to an SQL instance not running on port 1433, after som investigation, and thru the information i have in this blog: http://www.virtual-allan.com/microsoft-sql-database-restore-with-veeam-backup-replicator-8-0/ saying that the SQL Browser service should be accessible.
The customer returned to me that they found the solution, that UDP port 1434 also needs to be opened. this i not mentioned directly in the documentation, at the moment.
The link: https://msdn.microsoft.com/en-us/library/cc646023.aspx#BKMK_ssde they have in the documentation from Microsoft also tells that the SQL Browser Service is using UDP port 1434.