So, because I corrected your inaccuracies, I apparently need a clue.
Great job, Soro. Great job.
Oh, and don't forget that, while the aura is shown, what is causing the aura (which spell exactly, in other words), is not. A Necromancy aura? Only clue that it's not False Life is that it's 4th-6th level. What's to say it isn't Karmic Retribution instead? For all the White knows without careful study, that's what's on any of the Dominated folks, which is both a strong deterrent (doesn't want to be stunned for atacking the thing) and an incentive (the spell is Personal range, so if they have it active, it means they're capable of decently high-level magic) to focus that target.
Net result with Arcane Sight: The Dragon knows they have magic stuff and spellcasters among them. Now to go any further, it must test or study individuals, both of which take time.
Recall that Spellcraft requires the ability to "see or detect the effects of the spell" to identify it. Knowing of the spell's presence (and school) are not enough.