I've *NEVER* seen this happen in D3, only in WoW, but if an actual, flesh and blood, live GM wanted to talk to you, a purple line (not sure if it is in Diablo) with a blue "Blizz" logo would come across your screen, and inform you that a Blizzard rep would like to speak to you, please "click here" to begin chatting. Now that's the way it works in WoW, and I'm fairly certain should a GM bother to speak to you in D3 (and I"ve been playing since launch and never had this happen, as I said), I would assume that something similar would occur. They would NOT attempt to friend you through BattleTag or RealID. If they're concerned you're botting, they have other ways to watch you without friending you or even chatting with you in game.
We all are concerned somewhere in the back of our minds that our accounts may be closed, but if you're truly worried about the banhammer, and the account is indeed that valuable to you, don't bot. Or if you do, bot SMART. Don't let your bot go days unattended, or let it run in circles for hours in an open rift, or enter/exit games multiple times, etc etc. Common sense.