From what I've read there is little benefit from conventional vaccination against the weaponized "black smallpox" strains (purpura variolosa, also called hemorrhagic smallpox).
[Smallpox, bioterrorism agent]
From those links which I just read, prior vaccination confers some survival advantage, and hemorrhagic smallpox is not a strain selected for weaponization, but a particular clinical manifestation that is genetically predisposed for a fatal outcome. It's hallmark is a low platelet count, i.e. thrombocytopenia which can be caused by less platelet production by the bone marrow, less free platelets available because of consumption in blood clot formation and simultaneous phenomena.