You're totally right.. I will fix that asap.
I was working on a local branch to add persistence support for the app.
That orm.xml file is for the task related queries. And it's an exact copy of the file located inside the jbpm-human-task module. If you look in the jbpm5 source code you will find a different orm.xml file containg the ProcessInstancesWaitingForEvent query. That file can be located under the the *-persistence-jpa module. Check: https://github.com/krisv/jbpm/blob/master/jbpm-persistence-jpa/src/test/resources/META-INF/orm.xml
If you merge both files you can just have one orm.xml file.
Greetings.