Worth noting on this that while sync works, copy is the much safer option.
rclone copy source:/path dest:/path is what I'll likely end up using. In any case, the resulting solution still works.
Still need to tweak OSX a bit as it seems to kill the SSH session after some time for sporadic reasons - still testing but I may end up having to add ServerAliveInterval 120 to /etc/ssh/ssh_config to resolve that issue.
Then if you do this how you do you check that the Backups are good or you just the tar archive.
You'd untar them.
That is a full check. But without paying to download the file you just uploaded, you hash the file first and send the hash along with the upload. B2 will hash it when completed and verify that it matches your supplied hash. If it doesn’t, it asks it to reupload.