Smallpox is terribly contagious. The Aralsk incident http://www.cns.miis.edu/pubs/opapers/op9/op9.pdf and http://cns.miis.edu/pubs/week/020729.htm proved that the Soviets had "weaponized" smallpox, aka made it distributable in aerosol form, but the fact that only one of the crew contracted smallpox is pretty good proof that this test did not involve the more persistent powdered form.
On the other hand, Ken Abilek, former deputy director of one of the major Soviet biowar programs (Biopreparat) has said repeatedly that the Soviets did succeed in creating a powdered form. See http://www.infowar.com/wmd/SaxtonJEC_hearings/wmd_052198d_j.html-ssi and his book, Biohazard.
Stupid people lingering in areas contaminated with former Soviet smallpox powder obtained by terrorists or, more likely, Iraqi-produced smallpowder, would be contagious once they catch smallpox from the powder. See an article on Strategy Page called Smallpox Apocalypse for what would happen then. http://www.strategypage.com/strategypolitics/articles/20020722.asp.
So yes, people who won't voluntarily evacuate areas contaminated with smallpox powder would likely be forced to leave, if necessary by being shot dead. You don't fool around with that kind of threat.