I have been experimenting with this.
Process seems to be that it saves a TIFF file which reflects the PR settings under the DXO program files in a Temp folder.
I could see a sublayer in PS which was white.
Now however the process is no longer completing. PS and DXO have full disk access.
Also I note of importance, this method does NOT give access to my own Presets and Camera Matching presets, whereas if I save to a DNG I have access to those. In that case if I want to change my PR settings I have to rerun it.
Assuming I can get the Open as Smart Object to work again, the lack of my own processing presets and the saved TIFF file (large HD usage) seem to be two major drawbacks.
