Just to put a few things straight, as far as the RAIB are concerned (who have spoke to me), there is no firm evidence to suggest that the driver was fatigued on the day. The driver did not say to anyone Official (Booking on Clerk, DSM etc) before booking on that he was fatigued on that day, so case closed in that respect. The RAIB have said that they are no longer investigating this incident and that the digest provides the relevant learning points.
Thus, unless the driver himself says that he was fatigued during the post incident interview (or medically proven), then they can't use that as a factor.
Of course, personally and as many others have pointed out, there is an issue in the industry where certain Muslim drivers fasting during Ramadam may feel that informing they are fatigued before booking on could lead to disciplinary action. It's been well documented that this was one of the worst Ramadam's on record in general amongst the Muslim population in the UK, hence all the press from the likes of the Daily Fail.
It would be down to the individual TOCs to manage this properly, without the fear of Fasting Muslims carrying out Safety Critical duties to avoid harming their career prospects while they are fatigued.
I don't think GWR or the RAIB have brushed this under the carpet to save political face in this instance.