Indeed they are not Guardians but they are dark equivalents, its pretty clear when you read about the differences between them. They are based on the same three ideals. Of course as Aurash becomes Oryx and grows in power and subsumes his siblings they become less distinct but especially in the early verses its rather obvious that they are meant to be metaphorical parallels. Sathona the "cutting mind" Xi Ro the "brave sister" who "yearns to become a Knight" and Aurash the "lonely navigator". Do those not sound like Warlock, Titan, and Hunter to you?