Just wanted to say thank you to Landmast0rz. Nothing else online helped, but this solved our problem. We didn't need the failOnWarning setting, but we did need to remove the <scope>test</scope>
Specifically, the integration test module had the app module as a test dependency. Once I removed that scope the aggregation started working. Still really confused about WHY that worked, but it worked.
Our project structure
app-parent
|- app
|- app-test
|- app-deployer