I’m not sure I am totally following what you are doing but I will try to answer.
Synchronization of Photo Libraries is handled by Apple, and works using iCloud Photos. Nitro does not have any ability to influence how that works.
When you are exporting from the file system to the Photo Library via Nitro, how are you doing that? If you are exporting a rendered image (e.g., a JPEG) then Nitro will make a new file with the edits “burned in” and add it to the photo library. The original is not copied into the library and the edits are not copied either.
If you export the original + metadata to the Photo Library, then Nitro will add the original, all Nitro metadata (including editing parameters) and the full size rendered image to the library. You can edit non-destructively and the edits etc will synch over iCloud if you are using iCloud Photo Library.