In comparison with foods preserved by other methods, like canning, it is quite safe. Botulism is feared in canning because the bacteria that cause it thrive in a liquid environment. Botulism could only occur with a dried food that had been rehydrated, then left unattended long enough for bacteria to grow.
Mold may form on dried food if it was not dehydrated long enough or if the container it was stored in had moisture in it. If you see or smell mold, all the food in that container must be discarded.
Remember that the organisms that cause food spoilage, mold, yeast, bacteria-are always present in the air, water, and soil. It is important to observe sanitary precautions at all stages of the drying process.
As to the safety of drying meats, the latest word from food-science researchers at the University of Wisconsin in Madison is that microorganisms are effectively killed when the internal temperature of meat reaches 145°F for 45 minutes; or 167°F for 20 minutes; or 200°F for 15 minutes. This means that the internal temperature of the meat must remain steady for the designated amount of time, which is not the same as putting meat in a 200°F oven for 15 minutes. If your food dehydrator does not reach a temperature of 145°F or if its temperature control is inaccurate, then transfer the food to a preheated 200°F oven for a minimum of 20 minutes to eliminate safety concerns.
You can also store dried food in the freezer, another form of ensuring its safety.