I'm happy enough for Mr. de Villiers to consider 'AB' to be his first name; Abraham Benjamin sounds too American presidential, and nobody wants to be associated with either Hillary Clinton or Donald Trump (or, when he came onto the international cricket scene, Dubya), so I bear no resentment to him going by his initials. His name, for all intents and purposes, is AB.
However, Burgey is entirely right that Mr. de Villiers cannot claim rights to 'AB' as a nickname due to the continued existence of the One True Living AB, Mr. Border. To claim AB as a nickname is borderline defamatory to the One True Living AB, however I'll give Mr. de Villiers a pass here because a) he's a sufficiently good batsman to not entirely tarnish the legacy of the nickname, and b) I do not believe he had malicious intent, or intent to use it as a nickname at all. I do not believe people who name their child 'AB' in honour and reverence to the One True Living AB should be putting their children in a situation where, if they become sufficiently good at cricket, they must change their name.
So, in summary, I believe the official nickname of Mr. de Villiers should be ABdV, or some variant thereof, that includes reference to his last name and not just his initials. But I cannot condemn him for utilising his initials as a name, because his name is, quite frankly, a bit ****.