Scott,
DensGlass Gold IS an exterior gypsum sheathing, it IS designed and intended to be installed directly to the studs with nothing behind it.
DensGlass Gold is also *not foam*, it is gypsum board with fiberglass sheets on its faces and edges instead of cellulose sheets (paper) on its faces and edges.
Added with edit:
However, for stucco, it should have paper-backed metal lath installed over it. However, it *does not* require a weather-resistive barrier, it already provides that purpose.
http://www.gp.com/build/documentview...entid=4922&bpl