I have recently been configuring a Synology RS815+ as a "Linux Repository" for Veeam. I found considerable information on Google that advised on doing a lot of things, especially making edits to the config onboard the NAS - that are completely unneeded.
To get it going this is all I had to do. From the Synology NAS web interface:
* Control Panel/Terminal & SNMP: Enable SSH
* Click on "Advanced Settings" and change the cipher strength to "Low" (Veeam doesn't support even the medium strength ciphers).
* Control Panel/File Services/FTP: Enable sFTP.
* Control Panel/User/Advanced: Enable the user home service.
* Control Panel/Shared Folder. Create a shared folder and grant "admin" access to it.
* Package Centre: Search for Perl. It will be listed under "Third Party". Click install.
Then in Veeam when you add the NAS, specify the IP address, tell it to login with the "admin" account. DO NOT select to use an elevated account, use sudo, or anything else. The "admin" account has access to everything it needs without any extra permissions.
Make sure when you select the directory in Veeam you select the same directory you created under "Control Panel/File Services" - the one that you granted "admin" access to.
Voila, everything is now working.