Yes, it is.
> Economics is about people assigning value to things.
People are not outside of physical reality, nor is their experience of utility.
So even if you accept the materialist position, for purposes of doing economics, you kind of have to regard humans as something different. (Or so it seems to me, a non-economist.)
If you have to strip away all uncertainty from the universe to support your position and further posit hard materialism and then qualify with “in practice it’s not discoverable but philosophically it’s there” then I feel we are squarely in angels dancing on pinheads territory.
Physics itself does not need such violent axioms to get useful results! I think you would be hard pressed to find a physicist who would claim a plausible conservation law for “subjective beauty” (another kind of value), yet this is also a consequence of your premises.
You’ve explained that you are a materialist but not really anything useful about economics as practised by humans. Who are, perforce, rather limited.
You could equally well say “there is a ‘true’ value for every thing, but only god knows it”. That statement would be exactly as useful and (as an aside) just as unprovable a belief.
But, in each step you are clearly adding more and more context along with the physical item itself, context that must itself have some physical encoding.
My point is mainly that I insist that physical reality is all there is, and if some events are hard to assign to any one physical thing that just means we are looking for subtle correlations.