That's a very distinct possiblity, that I personally find to be likely.  It would almost be a surprise if the Mexican and Brazilian specimens had identical chemotypes. And as whiterasta notes, there are all sorts of other poorly-understood variations in phytochemical concentrations.

Mimosa tenuiflora and Mimosa hostilis are synonyms, referring to the same species.  That's pretty well established in the literature.  It could be that specimens growing in different regions vary in chemotype (seems pretty likely), but there wouldn't be a seperate "hostilis" and "tenuiflora" chemotype, as both terms refer to the same plant, and aren't regionally associated.