This is a 3rd party container not validated nor endorsed by XO devs. We don't know what's inside, if you have questions on it, ask on the Github repo of the maintainer
Backup reports will answer your initial question/requirement (reports can be sent by email, Slack etc.) There's also a Nagios plugin, or you can use XO API to make request to be support in any software of your infrastructure
Monitoring a Docker container is outside scope of XO, I would suggest to ask Docker community.
Regarding XO and how backup are done, any fresh XOA deployed (or from the sources) will be able to find all the previous backup done by an old XOA, because we store every info on the remote.