Business Object is a BI tool that runs queries on data sources. Nuxeo repository can be seen as a data source for Business Object so as to build custom reports. This doesn't require specific integration, as all the data managed by the repository is “visible”, ie is stored in a comprehensible format. Each schemas (document properties) is mapped to an SQL Table. As long as you know how to query SQL, you'll be able to generate your report.

The BIRT integration relies on the same principle.