Slow cooking a whole raw ham will not dry it out. Leave the skin on and cook at aprox 275 deg F to 300 deg F. for aprox 8 hours.. Leave the skin on.. when you can tap the skin and most or all of the fat has dissolved or melted away, it is done. If you still have some time to go before serving, cover it tightly with foil and reduce the temp to 175 deg F. A whole pork shoulder or boston butt will cook well this was as well. Use your favorite rub or spice on the meat before you cook it. Slow cooking this way will make the meat melt in your mouth. When you cook a piece of meat this way the bone will not support the meat and it will literally "fall off the bone"
Slow cooking at a low temperature is safe,
We in the south have been slow cooking pulled pork that way for years.. what do think a crock pot does...
It would dry out in the oven but you could cook it in a crock pot over night
Is it a raw ham?...because most hams are precooked..and cooking one overnight... that is already cooked would just ruin it...........It just needs to be heated for 8 to 10 minutes per pound.........
It can be cooked overnight in an oven, but it would have to be fairly big. If it takes three hours at 350 degrees, it will take about 6 hours at 155 degrees.(you have to cook above 145 degrees).
I wouldn't do that. You'd need to have the oven at a low temperature to cook something overnight and low temperatures don't kill bacteria in meat.
"The USDA does not recommend cooking meat and poultry at oven temperatures lower than 325 °F because these foods could remain in the "Danger Zone" (temperatures of 40° to 140 °F) too long. Bacteria which may be present on these foods multiply rapidly at these temperatures. "
Most hams have been precooked so it is only a matter of heating them up, but I still wouldn't do this.
EDIT: @ Concerned--I live in the South, too, and if the USDA says it isn't safe, it isn't no matter what part of the country you live in! And, you have to use crock pots correctly or you are making bacteria soup!