Based on this discussion
The JaCoCo Maven plugin's Report goal doesn't allow to use classes from other modules.
Which effectively makes the report goal only usable for unit testing, not integration testing.
The report goal's configuration must be re-worked.
Other modules artifact's could be used for classes.
In case sources are needed too, the plugin could be provided certain path and it would load the project and scan all it's submodules for sources and classes.