Yes. Using specialised tools, such as SAP Data Services and SAP Landscape Transformation and the CDE features of SAP ILM, it is possible to extract data from non-SAP systems, map it to SAP or custom structures, and convert it into ADK files.
These files have the same structure as archive files created from native SAP data.
Once the data from the non-SAP system is processed, it can be used in the ILM Retention Warehouse in a similar way as native SAP data.
As non-SAP systems usually differ very much from SAP systems, expert consulting services accompany the decommissioning process to ensure a successful project.