Sorry for my recent absence from the discussions. Juggling far too much at once.
Now, getting to your question, yes, Sleep As Android can be sync’ed/exported to both Samsung Health and Google Fit smoothly if you wish to do so. Pretty much same data but the hubs try to analyze it in their own ways. Where SaA gets the data is up to your wearable. If your wearable can run a Sleep As Android watch app, you’re good to go for that. OR you can get Samsung wearable data into Google Fit! Here’s how. You needn’t worry about your Nest device for this, just your wearable if it runs Sleep As Android and can export to it. The Nest Hub seems to lack powerful features.
You need a neat little app called “Health Sync” that I stumbled over a few years ago. Install “Health Sync” on your phone. As best I recall, it’s free. Even if there was a humble little fee, it’s totally worth it. Follow the directions in the app and enable “sleep” syncing/importing/exporting from S.H. to OR from Google Fit. Your choice! Choose the direction you want your data to go. This is why you’d need Samsung Health as a conduit to Google Fit’s nifty sleep analysis. Samsung does a fair job of it, too. I like Fit’s analysis even better. I’ve been a bit busy lately but I try to keep this going every single day. It works automatically - no work to this. Make sure your data goes to S.H. and is sync’ed with it in SaA. Health Sync will do the rest after you tell Health Sync where to send the Samsung Health data. That’s up to you!
That’s basically it. The same sleep data can be everywhere and no extraneous data will be anywhere unless you want it to be.
You can’t see both SaA data and Samsung wearable data in the Fit app, but you CAN see them both elsewhere and decide what Fit will show you.
Hope this helps! The little app Health Sync will do what you want done, your way.
P.S. – To clarify, my wearable is not a Samsung. It’s an old Pebble Time. I don’t have an independent Samsung sleep source. It all comes from Sleep As Android for me. Pebble Health will track sleep independently AND send it up to Google Fit unless I stop it! I stop it. I do that to maintain the integrity of the statistics. I want SaA to keep the records and stats of it’s own data. And there are several independent sleep apps on my Pebble with the Rebble OS. I can have many apps tracking sleep. Just not Samsung or Withings, etc. But you NEED Samsung Health as your pipeline to Google Fit through "Health Sync.*