The regular rank and file that pour out (ones in red armor) are indeed real hive. They're the heretics. Regardless of them, the ones labeled "nightmare" may be pseudo apparaitions but they are physically manifested. They can actually kill you, unlike dream nightmares when you sleep. So, to say they're not real isn't true. They shooting and damaging you.

Vex simulations aren't real but their simulated bullets still explode your face when they hit you.

Simulation to the point of physical harm has always been an interesting aspect of Sci Fi. Same with death in a dream. Nightmare on Elm Street films would be a lead in that aspect of horror. So yeah, since Destiny straddles the lines between SciFi/fantasy/Lovecraftian horror, sure; real or not, physical or not, all our understandings of reality can be tossed. I suppose us discussing this is merely semantics.

Destiny doesn't straddle anything. It sits very firmly in the arena of Science Fantasy.