I think we are horribly confusing "truth" with "what we perceive/believe is true."
I firmly believe the existence of "truth" is independent of the seeker/observer of truth. Of course "what we believe is true" is always tied to who we are. So we have human physics, and human mathematics, etc.
In short, what we perceive to be truth is not truth.
Humans need symbols, and abstractions simply to perceive/interpret the truth. These symbols and abstractions are clumsy and inaccurate. We may need to inflate, exaggerate, abstract our descriptions of truth in an attempt to convey what we believe to be true more accurately. However, those inflations, exaggerations, and abstractions are not more true.
The truth exists outside of ourselves.
The existence of the universe was true before any humans (and human descriptions) were ever available. The existence of the inverse will be true when no human beings are left. jmo.
If a bus hits you without you seeing, hearing, feeling or perceiving it in anyway (suppose you were sufficiently anesthetized), can it still kill you?
It is my belief, that morality is the same way (though my confidence in this belief is less than that for truth).