@cloakadagger Not really. The ergot poisoning was more commonly found in France during this time period, IIRC. Which is why almost all the early werewolf stuff was a French/Norman introduction to Anglo-Saxon culture.
As Samhain was predominantly a Celtic festival, it would have been geographically only been celebrated in northern Scotland, Ireland, the Isles of the Irish Sea, some of the Shetlands, and northern Spain (Basque region).
Though if ergot poisoning is shown to be common in those areas as well, obvs that would counterdict my point.