There are no additional steps needed. Your add-to-app
module will work the same way as a full-Flutter app.
Whether you integrate using Android Studio, 
Gradle subproject or AARs,
transitive Android Gradle libraries are automatically
bundled as needed into your outer existing app.

B. Plugins needing project edits

Some plugins require you to make some edits to the
Android side of your project.

For example, the integration instructions for the
firebase_crashlytics plugin require manual
edits to your Android wrapper project’s build.gradle file.

For full-Flutter apps, these edits are done in your
Flutter project’s /android/ directory.

In the case of a Flutter module, there are only Dart
files in your module project. Perform those Android
Gradle file edits on your outer, existing Android
app rather than in your Flutter module.