Due diligence is about getting confirmation from sources other than the candidate about their credentials for the job at hand - these will either confirm or contradict the perceptions and opinions you have about the candidate and therefore give you a better understanding of their suitability.Picking a coach is opinion and preference. Due diligence isn't applicable, we didn't miss that he's an ex crim or something.
Gus simply does not do this - he runs off his own gut feeling. Sometimes that is great but it can cause some real clangers that could be averted with just a bit of checking. There are a couple of recent cases in point with regard to appointments of high ranking officials.
I don't know about Griffin's capabilities or suitability but I do know that it is sensible to check your thoughts on a candidate against those that have had previously worked with them or employed them.