Legal? In the U.S.? Sure, there aren't any laws against it. Most airlines have policies against it. You can ship most species of reptiles fedex, or with delta, using delta dash, with no inspections or paperwork, besides labeling the package "harmless reptile" and the actual species in. the package to comply with the lacy act.
Why does someone want snakes from the us? Why do er want snakes from brazil? Or indonesia? Or leopard geckos from pakistan? It's different and exotic. And there are primarily two subspecies of Boa constrictor in brazil, Boa constrictor constrictor, and Boa constrictor amarali. From what I've heard, he mostly had boa constrictor imperator morphs, hypos and such. And they can easily hybridize with other Boa subspecies, so I'd bet brazil wants nothing to do with them as captive pets. (Not that it every got to brazil or they had a say in it.)