Wade Davis has contributed some fascinating perspectives on anthropology and ethnobotany...though perhaps he's more of a big picture guy and lacks the scientific rigor required for gaining credibility as a 'serious researcher' in the Western world. I don't know enough to say for sure one way or the other.
However, in his defense, it doesn't seem that the tetrodotoxin hypothesis was the core element of his zombie interpretation, although from his wikipedia page, you'd guess that he'd claimed it as the crowning achievement of his entire career.
According to wikipedia, "TTX, which blocks sodium channels on the neural membrane, produces numbness, slurred speech, and possibly paralysis or even respiratory failure and death in severe cases. It is not known to produce the trance-like or “mental slave” state typical of zombies in Haitian mythology, or Davis’ descriptions."
From a quick search, however, it appears that Davis never claimed that TTX produces a trance state. Rather, he says that this phase of 'zombification' involves a culturally-specific psychological predisposition to possession (unique to the psyche of select groups of rural Haitians) often in combination with the use of the deliriant, datura. Davis seems to offer a more multifaceted argument than is appreciated by critics. According to a
book review, Davis' critics ignore much of his thesis and "pounce on the tetrodotoxin samples as the only issue to be considered."
My feeling is that Vodou zombies are likely the result of psychological rather than than pharmacological manipulation...but, regardless of the truth of the TTX hypothesis, Davis seems to have made many worthy contributions to the fields of anthropology and ethnobotany, which should not go unappreciated.
