Yes, you can mix both into one app. Like you said, you just need to write conditional workflows to hide the native page or redirect if the user is logged into the admin panel. Completely fine to have both on the same app as they will both share the same databases in Bubble.
Alternatively, you might build API endpoints from the native app to the admin app in order to keep them securely separated at scale.
@trujillo345 - if you want to host your database externally (SQL, DBaaS, etc.) that’s possible using Bubble’s API connector. I originally hosted all of my data externally, but eventually migrated everything into Bubble in order to save development time and optimize performance (i.e. speed the user experiences when using the app)…haven’t looked back since. That said, you just have to take note of limit rates with the service hosting your data and integrate pagination if needed…another reason I moved things to the Bubble side for simplicity sake. A “native app’s database” can be hosted anywhere, including Bubble (which is hosted on AWS and completely scalable).