I did a little bit of work to integrate with Dexcom’s CGM service, but thanks to the FDA they hold back the readings for an hour. Doing something in the home automation based on a blood sugar reading from an hour ago is pretty pointless so I dropped it. You can see what I did at OAuth2 using just OH Rules and myopenhab.org. Note that it was done years before OH 3. I’d implement it differently today.
Later we moved on to using Nightscout and had pretty good integration with it which you can find at NightScout openHAB Integration.
Since then we’ve moved to Tandem and because the integration with the home automation wasn’t all that useful over all I’ve not tried to reintegrate that. I think though that the Tandem app still supports Dexcom Share which could be used to push the readings to Nightscout. I haven’t looked beyond that though.
Note that Sleep as Android supports MQTT it’s possible to provide some good sleep tracking integration with openHAB. @rpwong posted a good tutorial on that at Sleep as Android and MQTT.
There have been posts here and there looking for Google Fit integration but I don’t know if anything has come of it. In general though, if it can integrate with Tasker on Android, it can be integrated with openHAB through the openHAB Android App’s Tasker plugin.