I completely disagree. Most of what you listed seems to be accounted for that these people are apparently completely untrained for the mission they're going on. Perhaps the person in charge of planning this was a complete idiot. More likely the mission has different goals than what they publicly stated. Maybe it was meant to be a test to look into the psychology of cloaking technology. Maybe it was meant to find out if there are alien mercs on the ground between these two bases. Maybe it was meant to find quality soldiers among the group, ones who would see the idiocy in the others' tactics and act in a way more likely to succeed (as Sweezy may have done)
If you actually wanted to plausibly test this technology for usefulness, you'd take one highly trained and heavily psych-screened commando without weapons and send him alone with limited supplies so that he would have no choice but to go to the other hatch in x days. If he didn't arrive in 2*x days, send another one separately with a similar time constraint. If he didn't arrive, send one more. If none of them arrive, then your test has failed.
Putting them in a squad just encourages paranoia, with no benefit. And giving them guns makes no sense. You're giving a man an invisible gun to shoot at invisible enemies among invisible allies. How the heck are you supposed to do that properly? Putting them in a squad and encouraging them to sound off to each other is just going to attract enemies, with no real benefit. Unless the planner of this mission was a complete and total tactical idiot, these men were not meant to survive.
This story was a work of genius. Too bad it was originally published in 2002, or I'd nominate it for a Hugo/Nebula.
You knew a list was coming. Here it is. The reason I liked the story is that there were at least 3 completely plausible interpretations, based on the text of the story:
1. Sweezy survived, and saved him from the alien, as the Sweezy voice explains. If any one person was going to survive it would be Sweezy. The story did well trying to give the wrong impression of him, trying to make him seem an unprofessional whiny runt of the group, but it occurred to me early on that he had the right tactic of NOT sounding off. Sounding off makes you a target for the invisible enemy, and gives you little benefit in return. So it makes sense that he would take the first advantage he could when an alien uncloaked. It perhaps doesn't make sense that he would THEN reveal himself, because then he exposes himself to a second alien merc. But maybe he just got overconfident.
2. The protagonist's suspicions are correct and Sweezy has been taken as well. Although Sweezy has seemed smarter than the others not to sound off, that doesn't mean that the aliens don't have other ways of sensing them. Feeling for the vibrations of their footsteps through the ground, or the sound of their boots. Sonar would probably reveal their shapes sticking up from the ground. Or other spectrums of light like infrared or ultraviolet. They have no idea how the aliens natural senses work, let alone how their tech works, so its very possible that the visible cloaking has no effect at all. The alien voice claimed that it liked to toy with its victims, so pretending to be Sweezy could just be an extension of that, stringing this guy along more and more, maybe to try to infiltrate the base at the end or maybe just to mess with him.
3. The protagonist has been separated from the group, has gotten lost, and has not been anywhere near anyone else. They haven't been trained properly for this mission, and so it wouldn't surprise me at all if they also hadn't been psych-screened. Or had been psych-screened and he was chosen specifically because he had psychological problems. I don't know that I understand schizophrenia very well, but it seems to me that this character could've been living with a latent schizophrenia that he had learned to cope with. But in a stressful life-and-death multiple day mission where he is in a situation where it is entirely plausible and indeed expected to hear voices in his head without seeing people speaking, that he has lost his ability to cope. As a soldier he is trying to anticipate all the crap that could go horribly wrong in this terrible, untrained mission doomed to failure. Because he's trying to anticipate it, the sounds of dying and the voices of his friends and then the alien are all just part of his mind playing out the scenario.