Confirmed that this works.
I keep a backup of the config directory for each server, just the config.xml, cert.pem and key.pem. Beware that if someone else acquires these files they will have access to all the files of every connected device.
Each of my Syncthing servers in a cluster sends their config to one another, setup as a send-only set from each server, send-receive on the others (Ignoring *.db, *.ldb, *.log).
The database files are not as important, they can be rebuilt and it is risky to restore them if there have been files changed since they were backed up.
See also this discussion: How to save configuration of Syncthing