Well until Shaman’s connections to Spirit and Decay was chucked in the trash, we would have absolutely been able to make deals with the denizens of both those domains. Shamans would have been perfectly fine back in Vanilla, we’d just sub our Fire Ele for a Death one or some powerful ancestral spirits and BAM! Though in their current “ONLY the 4 Elements” form you could just equate what they’re doing to what Warlocks do. They just call upon contract Elementals rather than Demons.
As for Druids, I would assume they can do their thing for the same reason Priests and Paladins of every sect can still do theirs? That those Cosmological Forces aren’t completely absent even in the realms of Death?