Confused with Photos—maintaining my own folder structure for photo files

No, Photos cannot do this. You can keep the original image files in a folder structure on your Mac, but the edited version are stored inside the Photos Library and not accessible in the Finder. When you edit a photo, Photos will just store the sequence of adjustments to be applied and create a preview of the edited version for the Media Browser. The final edited version will only be rendered when you export the photo from Photos. Edited versions are living in limbo in Photos. This will save storage and ensure a high quality of the final edited version, since the edits will always start from the high resolution original.

You need a different photo organizer, if you want the edited versions organized in Folders in the Finder.

He could export the edited version as a high-res jpeg or TIFF to the desired folder. But that is cumbersome and takes up lots of space. This would not work well except for very occasional edits. I would just trust Photos.