Hmmmmmm.....
The old 'use a fader of a quality plug in's gain control ploy' (with an added buss spin)
The person that can really answer this will have a DEEP and UP TO DATE understanding of the developments of the Pro Tools mixer. (for it has at various times been tweaked) One thing that enshrouds the issue in darkness is perhaps an 'it was created perfect' vibe from it's maker Digidesign. From their lack of comment on the mixers sound, one assumes that they feel any announcement of improvement would point to there in fact being a 'problem' in the first place and so the cycle of double think, cultured in darkness goes round and round.
Well, however it was created, it HAS been tweaked in the Mix platform AND HD and that can only be good news.
I DO believe that using the 'dithered mixer' might make the practice my good friend Mr. Glasgow follows redundant but then I don't have the deep understanding of the PT mixer and it's various stages of evolvement necessary to comment conclusively.
How is that for a long 'I don't know" ?