The PDF manual (p.51) says image "rotations are only performed 'visually'" and "is in line with Photo Mechanic's policy of never altering the original image data in any way".
However, when I rotate an image in PM and use the 'e'dit command, it shows up rotated in Photoshop.
Are you making a temporary copy of the to-be-edited image, rotating that and then passing Photoshop a path to this temporary image?