'If so, it seems as though one could induce inadvertant barrel rolls with a fully articulated rotor, at the very least!'
No. An articulated head will have sufficient control power to maintain control in roll even under negative G. A teetering head relies on positive G to provide control of the head. Having said that, apart from turbulence and gentle push-overs when low level at fast cruise, negative G is a no-no (IMHO) with 350s, or with any other for that matter.