Just off the top of my head, applications can watch for files in at least three different ways;
1) An EVENT type of job object (there are multiple types so you'd need a filter).
2) As a workflow task precondition rule.
3) Custom script logic.
I suppose one could figure out how to search for each three types and combine the three result sets. But not exactly trivial. Some of these searches would have to be done with SQL directly against the UC4 database.
Is this request worth the effort? What will the information be used for?