Polyglot profiles are stored on ISY/IoX. But actual polyglot DBs aren't. PG2 is in MongoDB and PG3 is in sqlite. I, personally, don't think it's a huge deal if I had to reinstall node servers from scratch. But if you're thinking of full backup, you should include it.
rsync is basically network copy. You would normally have another machine or NAS drive running rsync server and then you configure a script to copy any files you want over rsync to that device. That's an automated way.