The darkspawn scavenge their armor from the Deep Roads, from lost thaigs and from battlefields where vast armies once clashed. Typically, only hurlocks, shrieks, and genlocks wear any such protection, ogres being far too large for conventional armor.
But occasionally the Legion encounters ogres wearing crude patchworks of breastplates and shields threaded together with rope and wire. While better than nothing, there are many vulnerable gaps in the assemblage. Thank the ancestors that the darkspawn and their ghouls make such lousy craftsmen.