I was successfully able use the "cm.sys.state" event containing the "SAVE_COMPLETE" message while confirming that the configuration database was, in fact, the file saved using the latest "show switch" output. This was a bit convoluted and required enabling log debug-mode, but it worked.
It is unfortunate that EXOS does not provide more specific logging messages related to overwriting the configuration database. The data for that are available in EXOS as it does update the information displayed by the "show switch" command. However, the ems process does not take advantage of that currently.
I could not use the cli-config-logging events because when the operator issues a "save" command from the CLI, EXOS presents one or more confirmation questions whereby one can cancel the command, choose not to affect the configuration database, or delay its action. That, and there are types of "save" commands that do not involve the configuration database at all (e.g. save config as-script). These factors made pursuing that avenue impossible.
I may open a feature request for more specific log messages regarding the overwriting of the configuration database. It seems like something that would be very useful for auditing configuration changes, and I wouldn't be surprised if our more "compliance-centric" customers (Hospitals, Governmental, Banking, etc) have already requested such a feature.