With DP8 and 9 you could try to tap into the Postgres-DB and extract the Data from there, but there is no official API or ODBC Interface yet, same with DP 7 and below.
HP Backup Navigator extracts many infos from multiple Cells and handles them in a own DB that might be easier to be accessed. Used MySQL/MariaDB at one point, not sure if that is still the case with current release.
On our Cells we use a combination of omnirpt Reports list_sessions and session_objects to cover most of the Reporting needs.