Causation need not always define effect. While the methods of fear in D&D may undergo taxonomy for simplification, the end result of their application is still avoided only via will save or immunity. While this specific non-magical fear is categorized as an extraordinary ability, it is still the result of extraordinary *circumstances* stemming from looking upon a rather extraordinary-looking dragon. Without either a magical or psionic conduit to artificially instill this fear, I fail to see how extraordinary-ability fear differs from any other naturally occuring type of fear one would experience. If this aura persists in no-magic zones, then one would assume that its source was entirely situational to the amount of fearful stimuli witnessed by the viewer.
Extraordinary abilities are nonmagical, though they may break the laws of physics. They are not something that just anyone can do or even learn to do without extensive training.
I'm surprised no one's really brought up the converse situation, where you RP your attempt to intimidate someone really well, and by all reasonable accounting, the character you're attempting to intimidate should be intimidated, but doesn't even so much as acknowledge it, except to boldly act as though even if Vorax himself were the one trying to intimidate them they wouldn't back-down.So, in the end after reading these kinds of posts time-and-again, I say the need to roll or not roll greatly depends upon the players involved in any given situation and their ability to maturely handle it and either acquiesce one to the other, or agree to rolling to settle it.