Grim alliances...
I dont think the empire would like unsc very much...
No, but their technical proficiency might be indispensible. So basically just Mars again.
As someone who was at very much into halo lore but who is just a little 40k curious, can I ask why? The UNSC is basicly pure uncorrupted humans fighting aliens. To my beginners eye it seems like they would get along.
Unsc uses AIs which is a big 'no no' for the empire
Lack of faith in the emperor.
Foul xenos!!!!