I can't imagine trying to read a map without any kind of legend, documentation, or grid references. Trying to do so in the middle of any kind of battle or large scale maneuvering boggles the mind. It just doesn't make sense to me that any kind of military could function without any of its members being able to read. Relaying information and/or orders without writing would be a recipe for disaster. A single word could mean a world of difference.
Even in a society where by custom men don't read, the military would have to have a specialized department that would be literate. The military might be able to get away with using women and ardents for logistics but not for scouting, relaying orders, and map reading in the field.