Whilst contacts saved in a .csv file can be imported to Samsung Kies and synced with your device, it is unlikely you could directly import them to a .ssn backup. At best you can sync them with your phone and then perform a full backup of your device using Samsung Kies.
Convert Comma Separated Value to Samsung Kies notes backup file.
We found 2 software records in the database related to .csv to .ssn file format conversion.
Microsoft Windows software - convert csv to ssn on Windows
A free software for managing of latest Samsung mobile devices
Convert from csv file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned csv to ssn. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert csv to ssn on OS X
Management and sync utility for Samsung mobile devices