I have certainly known of cases with cracked Main Rotor Hubs, and I believe it is a "known issue".
From an engineering point of view if MD are saying that they are O.K, what is the problem. If the hubs are being returned as "cracked" on the paperwork I can't see what the problem is if MD assess them as being serviceable. Obviously I don't know the whole story or the details of the cracks, but that would be my initial reaction.
"Mad as a mooing fish!"