This a theory of mine. The first (obvious) evidence is that the masks on solstheim look much different than the normal ones (all tentacle like). The second is that the masks are daedric and benefit from the perk. The priests all also have shrines to herma-mora. Dukaans name means dishonor,and it's possible that he was involved in miraaks uprising. My last evidence is that the other named dragon priest vahlok the jailer who was possibly the only loyal priest had no mask.
How plausible is this theory? And is there any other evidence to improve upon/ disprove this theory?