I'm not exactly sure of your circumstances, but this sounds doable.
The public React Native API allows you to expose arbitrary pre-existing Views and expose new native functionality in modules accessible from JS. These can be written in java (or in C/C++ and exposed via JNI -- and if you structure your code properly you can also share that native module with an iOS RN app if you'd like).
We also support having just part of the app, e.g. some of the screens, written with React Native. This is what we do with the Groups app.
The main thing to be aware of is that splitting app logic and data management between JS and native will mean that you need to be careful with cache consistency between the two.
The public React Native API allows you to expose arbitrary pre-existing Views and expose new native functionality in modules accessible from JS. These can be written in java (or in C/C++ and exposed via JNI -- and if you structure your code properly you can also share that native module with an iOS RN app if you'd like).
We also support having just part of the app, e.g. some of the screens, written with React Native. This is what we do with the Groups app.
The main thing to be aware of is that splitting app logic and data management between JS and native will mean that you need to be careful with cache consistency between the two.