While using --plugins Java with a java RPM I got the same message at issues report than without invoking the plugin:

{{{
- This seems like a Java package, please install fedora-review-plugin-java to get additional checks

}}}

invoking fedora-review with -v seems to confirm everything is correct:

{{{
...
DEBUG: plugins: {'Java': True}
...
DEBUG: plugins_arg: Java
...
INFO: Active plugins: Generic, Shell-api, Java
...

}}}

As a reviewer I would expect the message not to be reported if the plugin has been activated (no matter if automátically or explicit in CLI).