Bubba Watson ain't got nothing on this shoulder turn!
To be fair I would say on iron shots his right foot was pretty square (from the videos I've seen). He definitely flared it on longer clubs though (below). I'm a big fan of foot flares but I will say that it's not "required" to flare you rear foot in order to perform an effective backswing. It just makes a few things much easier. The benefits that come with flaring the rear foot: centered hip turn, turning the hips steep enough, banking the right foot on the downswing, Hogan didn't need "help" with this stuff.