I don't mean to pretend I know anything about yeasts, but I think the discussion in this thread is somewhat problematic in two ways:
First, the notion of a "Saison strain" itself. The definition and vaguely historical connection of Saison as a "beer style" is shaky at best, so what does it mean for a strain to be "a Saison strain"? A yeast that originates from an ancient farmhouse brewery? Or just a yeast that can produce a beer that you might pass off as a Saison? In the latter case, I think the Achouffe yeast certainly qualifies, with its intense fruity and spicy character. In spite of its "normal" attenuation, it produces a much drier beer than some "French Saison" strains, in particular Belle Saison.
I mean, this entire thread is based on the observation that La Chouffe is pretty saison-y in many ways, even if pretty boozy.
Second, some posts here immediately jump to genetic similarities and family trees. This appears to take for granted that we answered the question above with some form of ancestry and family relationship between Saison strains, although I don't think it is necessarily a given that the yeasts used in 19th century Belgian farmhouse breweries - if these even were a thing - were all closely related to one another.
And just to repeat a point that has been made countless times whenever these family trees are discussed: genetic similarity and phenotypical similarity are not the same thing.
That concludes my party-pooping for the day. TL

R the Achouffe yeast is an amazing strain that can also be used to make Saison-Style beers. I don't know if there is a meaningful way to discuss whether that makes it "a Saison strain" or not.