Since smallpox has been eradicated from the planet, thanks to DA Henderson, the human population has little to no immunity to this deadly pathogen. This fact is what prompts concern about its use as a bioweapon.
In lectures, I often say that one case of smallpox represents a likely bioterror event. However, a recent paper published in Emerging Infectious Diseases details the ability of smallpox to persist in relics (corpses, scabs).
The conclusion of this interesting paper is that historical relics do not pose a major threat of smallpox exposure as infectious viral particles have not been recovered from myriad samples, though viral DNA has been discovered.
So grave-robbers are likely safe from this pathogen.