I just assumed that any Halo character’s theme in any crossover appearance would be the main theme (unless they have their own leitmotif that I don’t know about), but from what I have heard of Arbiter’s theme it doesn’t sound like that. Anyone know what it’s supposed to be? A remix? A new composition.
Also note that I haven’t played Halo 5: Guardians so if it’s a remix of a track from that then I never would’ve been able to recognize it myself.