Since the local server backup does not require any login like SFTP/FTP does,
will I be able to use WinSCP to backup remote server?
I'm not sure what your question is.
Are you asking, if WinSCP can backup files from an SFTP/FTP server to a local machine? Yes it can.
Finally, taking it for granted that everything works as it should,
Would I need to purchase a license in order to use this technology in my application for commercial use?
No. WinSCP is GPL software: