The accusation of nepotism is kind of hilarious. As if managers in the business world only ever hire employees they have no prior relationship with. When a company hires a VP, and the CEO knows the candidate, does he recuse himself from the process and leave the therm when decision is being made? I doubt it.
Secondly, as to Cummings' non play calling role at his previous job - if you think this reflects poorly on Diaco's judgement, the implicit assumption is that this took place during the interview :
BD : You didn't call plays last year but you must have have ideas of your own. Tell me what your philosophy on play calling would be.
MC : Herp derpy derp de derp!
BD: Good enough for me! You're hired!