drools-maven-plugin-example is not built as part of the parent build. It's broken.

Updating the src/main/resources/META-INF/kmodule.xml file to have a namespace declaration fixes the immediate error:

<!-- Add xmlns attribute -->
<kmodule xmlns="http://jboss.org/kie/6.0.0/kmodule">
</kmodule>

When that's done, a simple .jar file is produced. The .drl files are not compiled.

There's no significant documentation for the drools-maven-plugin except for its precursor: http://passion.forco.de/content/maven-drools-plugin. It's not clear what the objectives of the plugin are.