You won't really like the answers. I was curious so I made a test case Aperture database and transferred it over to Photos.
All changes, such as the +0.5 exposure, any brushes, and any adjustments made that are not in Photos are brought across.
It appears that you can revert to original or made additional changes, but these are additive to the imported file. So in Photos you would not see that the exposure was adjusted +0.5 in aperture (only that adjustments were made to the original), but you could apply an additional 0.5 adjustment.
While the brush application is there, there is no indication that it was applied.
Basically you see an image (which has whatever Aperture did applied) but all the adjustment controls are in "neutral". It does seem that any adjustment controls that are optional in Photos but were used also appear but are in "neutral". There is a revert button that appears so that you can undo the Aperture editing, but you don't know what the editing was!
You are welcome!
That is true. The RAW fine tuning controls are not available. It works like iPhoto.