Can I generate a report to display data from multiple application objects?

Yes. While building a report, you need to select an application object. If there are any application objects to which the selected object is related, you can use the fields from those objects in your report.
If there are no related objects for the selected application object, you can define a relation between the application objects. Check out the application object from the application object repository and click Object Constraints to define a relation constraint.