All clinical types of smallpox, including hemorrhagic smallpox, are caused by the same Variola strains (i.e., either Variola major or Variola minor). There is no good evidence that hemorrhagic smallpox was caused by a more virulent strain. There are numerous example in the literature showing serial transmission of smallpox with different clinical types. In the broadcast, we showed pictures of a child with confluent smallpox passing to a woman who had modified smallpox who passed it to her husband who died from hemorrhagic smallpox (pix from Christies chapter on smallpox in his 2nd ed. Infectious Diseases). The clinical type of smallpox is probably dependent on host factors. Hemorrhagic smallpox is a rare clinical type of smallpox and is probably related to immune deficiency.
In Rao's clinical series (reported in Fenner et al, Eradication of Smallpox), a history of vaccination did not provide protection against hemorrhagic smallpox - i.e., the death rate was the same (>95%) for unvaccinated and for those with a history of vaccination. However, history of vaccination meant only that the person had a vaccination scar. There was no data on how recent the vaccination was. Most of the people in that series probably had been vaccinated in childhood, some 20-50 yr previously.
Bottom line - The smallpox vaccine is effective against both strains of smallpox. If a person has a positive take after vaccination, he should be protected against smallpox for a minimum of three years.