What happens with Overseer of the Damned in the case of a board wipe? I know that all the creatures die at the same time, so do I still get zombies or is that ability mulled by the fact that Overseer is now gone?
Assuming your opponent had two copies of Grizzly Bear it would result in all three creatures being destroyed and afterwards you placing two 2/2 Black Zombie creature tokens into play tapped.
Overseer of the Damned has a triggered ability which is placed onto the stack the next time a player would get priority. Put more succinctly, the ability doesn't go onto the stack until after the board wipe has finished resolving.