Orthanc tries and complies with the DICOM standard. So, any DICOM client should be able to Query/Retrieve against Orthanc.
Unfortunately, because eFilm is not an open-source product, we cannot conduct any test to ensure the proper connection between eFilm and Orthanc. If you experience any difficulty, you can work on a patch for us to integrate inside Orthanc.
Regards,
Sébastien-