We have enough story clues to determine that the creatures (1) breathe (2) have brain function (3) have some degree of functional circulation, implying a beating heart (4) retain some of the same metabolic functions as humans
Michael's anesthesia experiments during the GPS tagging confirm all of the above. For gas anesthesia to work you have to breathe it in, transfer it to circulation via gas exchange in the lungs, transfer the drug to the brain & body via the circulation. The creatures rapidly adapted to the drug which indicates some hepatic or renal function (again proving circulation as a corollary) as drugs are typically metabolized and excreted via a combination of those two systems.
Therefore, the creatures are not "zombies" in the traditional dead sense of the word. They are alive in some sense, just not normal humans.
This works from a physiology standpoint. Does it work according to the rules of Kc's universe? I think so. It's right there in the story.
Or have I got it all wrong?