If blizzard was completely okay with AFKing in the BGs/Arenas they never would have came up with the new report feature in BGs. To me that shows a clear stance on blizzards part...against AFKing. Will they perma ban your account for it? I doubt it - but it's more than definately against the rules.
And, honestly, whether it's against the rules or not, its against moral judgement and common sense. The teams you are going against want to play a game, they want to be challenged and feel the rush of victory, or learn from the shame of defeat. They don't want to wail on some pixels just standing there.
It doesn't make sense simply because you say your main focus is PvE. PvP gear isn't very good for PvE. It's better than random greens/blues, but if you spent a comparable amount of time in PvE as you will be spending AFKing PvP (and the lolamount of arena points you're going to get) you'd have a much better set of gear that is tuned to what you want to do.
I'd feel cheap getting something handed to me for doing nothing, anyway. What would be the point of getting the gear if I did NOTHING to earn it.