I guess it depends on what you mean by "objective".
I think the matter of objectivity and subjectivity, in particular the individual definitions/meanings of such things, are a theme that's pretty core to TSA and I suspect there will be some kind of reckoning regarding the nature of these concepts actually function in Earwa, come TUC.
As a result I'm of two minds about the halo's "being real". I do think there's an element of mass hysteria/delusion involved (somewhat only because I think that applies to basically everything in the series), but I think it may also be a commentary on that sort of thing, since we've been shown (repeatedly) what we as people from the Real World assume to be religious-mumbo-jumbo ends up being REAL in Earwa. Places are actually haunted. Gods actually exist, and frequently intervene with mundane life.
Earwa is intrinsically a meaningful place. There, “madness” or “being crazy” straight up do not have the same cost-benefit ratio that they do IRL, at least not for now. A schizophrenic in our world makes connections that don't actually exist because our universe lacks any intrinsic meaning at all (in theory). In Earwa, everything has meaning, everything is bundled up with meaningfulness – lunacy, in some capacity at least, allows one to see things “more clearly” I think, but perhaps only on a higher level, and at the expense of clarity for the “mundane”, everyday world.
Also, two things stand out from TGO for me:
At one point, Kellhus looks down to the haloes and ponders "how difficult to explain they are". This doesn't really jive for me if it's just another belief-makes-real situation, which at this stage of the series is, relatively-speaking, not particularly difficult to explain to either the audience or the characters (such as Proyas), especially by TGO where the philosophy is on steroids.
Secondly, Kellhus also ruminates on how the walls of the eleven pole chamber are deliberately black to make the haloes more obvious or apparent. If the haloes are completely false and exist only in the minds of people, then this would be pointless. The haloes would be as bright as the person believed them to be.
My idea as to the strange qualities of the haloes (and the reason they cast no light) is because they are akin to the way Cnaiur's strange “overlapping” appearance as Ciphrang. Whatever the haloes are, they are like a shadow of Kellhus's future/destiny, which exists atemporally as all things related to the Outside do.