If you try to configure the Eclipse Checkstyle plugin on any project uses the RAT plugin, then it will fail the apache-rat:check goal automatically. This is because the Eclipse plugin generates a hidden file (.checkstyle) which will not have the required licence file. Since this file is not part of the artifact produced, it should be excluded from consideration by RAT. I used the Maven Clean plugin to reproduce this but any project that uses the RAT plugin will suffice.
Impact: Cannot use work on projects that depend on the RAT plugin in Eclipse if the Eclipse Checkstyle plugin is used.
Fix: Add .checkstyle to the list of exclusions. Build RAT with attached patch and rebuild Clean plugin with it. This is a short-term fix. A better fix would be to design a way register exclusions with RAT (eg Eclipse Checkstyle could register .checkstyle).