Long explanation coming:
Regardless of whether they made it into the game, the masks remain a very dunmeri cultural concept. To the Dunmer, Daedra worship (more specifically, Daedra as aspects of existence) was at the foundation of their way of life -it makes sense for this to be reflected in the garb of their society's upper class - for a leading warrior or politician to don the appearance of the Daedra ans assume its aspect. To the Nibenese, Daedra worship is more incidental, a result of their cosmopolitan attitude and casual worship totems, spirits and foreign or domestic gods.
The government takes part in this by promoting its own selection of patron deities, mostly the Nine Divines and hero-cults like those of Reman, Tiber Septim, Morihaus or Alessia. Beyond the social sphere, however, we have repeatedly been told that the role of religion in political and military matters is very limited - due to Imperial distrust of Marukhati-style theocracies. In this case, it is very unlikely for any official figure to publicly assume the aspect of a Daedra, certainly not in battle. Of course, a battlemage may well be a Dagonite, but this would not carry over to his official function. At least, that's how I see it, and this is the way in which I think we can best distinguish Imperial Daedra worship from Dunmeri Daedra worship.
There is, I think, a difference between a Niben aristocratic battlemage, and the battlemage as part of the Legion. The former is an ancient caste, formed in the early years of the Alessian Empire, who hold power in the Nibenay as a kind of land-owning gentry. In the same way that medieval knights started out as cavalry units to be summoned by their liege, and ended up a political and cultural institution whose characteristics have little to do with their military value. A modern Niben battlemage, then, is primarily a governor and a landowner. His magical prowess and equipment are a matter of privilege, signs of office, and their practical use is secondary. The battlemage as part of the modern Imperial Legion, however, is something we see more of in Battlespire: he or she is an elite soldier (of any race) following a legion training program in a special complex in outer space - a special branch of the Legion, with a military personality and culture.
As I said, I like the design, and looking at it again I see how you incorporated elements of vanilla armor in an interesting fashion. But to me it feels like a kind of Nibenese shock trooper or berserker, not an elite armored spellcaster. Battlemage equipment should imply something of their weird off-world activities of recent years: their connection to the Battlespire, their role as officers, their appellation of "the Shadow Legion". Also, something that's somewhat besides the point, but your choice of Mehrunes Dagon as mask made me question the concept quite a bit: Dagon is the one who conspired with Tharn, imprisoned the Emperor during the Simulacrum and destroyed the Battlespire. I don't think his visage would be too popular among battlemages right now.
Anyway, back to masks. Allow me to propose an alternative concept: instead of the Daedra, battlemages and other warriors could wear masks depicting aspects of the Nibenese totem animals: the bull, the snake, the tiger, the moth, ... This would ground the idea in specifically Nibenese cultural terms, and ally the wearer to Empire-friendly spirits.