There is no minimum quality requirement for scans submitted into the DCS. You can continue to upload scans that are the quality and format your institution has previously used.
If a scan made by another institution is available when creating a link to content, you will not be required to use the scan if it is not up to the standard of your institution. You will always be able to upload your own should you wish to.
OCR compliant scanning is not compulsory. If another HEI has uploaded the scan that you need but it is not OCR compliant you do not have to use this scan.
If you are ordering from EHESS through the DCS, the file will be delivered to you via the DCS. If you would like to amend the file to make it screen readable (beyond just OCR, which EHESS files come as standard), you can download it, amend it and then re-upload it.