Much as I appreciate the original author's analysis, he's trying to shoehorn logic into an illogicial situation. Put another way, "Fredo's men" wins by default, a process of elimination--but default or process of elimination doesn't resolve the illogic of the situation:

We know that Roth was behind the Tahoe attack. If Roth wanted the shooters to survive so they wouldn't be captured and be forced to squeal (an idea that the shooters would have warmly endorsed and insisted on, since it involved their survival), why wouldn't he--and they--have worked out an escape plan for them? Relying on other, unknown killers (Fredo's men?) to kill the shooters would have perpetuated the problem: how would the throat-cutters have escaped detection? And, if they were "Fredo's men," having them as the last link in the chain leading to the shooting would have brought suspicion that much closer--a lot closer--to Fredo.

FFC and Puzo were engaging in dramatic license. They left us with the mystery of who killed the Tahoe shooters to underscore the dramatic precariousness of Michael's situation at that moment ("...killed by someone very close to us...very scary..."), and to justify his immediate departure from the compound so he could meet with Roth, Pentangeli, go to Cuba, etc.--all in aid of discovering that Fredo was the traitor. The important thing was that Fredo was ultimately exposed as the traitor--not who killed the Tahoe shooters, which was just a filmic device to set the next (absolutely brilliant) sequences in motion.