I have not used openkit yet but if I'm not mistaken based on the documentation DEM and also DDU can be required for openkit instrumentation. DEM eg. for custom app instumentation or DDU eg. report a business event.
I hope it helps.
Correct - but it's only the case if you are using business events, and you are sending data to Grail-enabled SaaS tenant.
All other features consume DEM only.