The Hornady zombie rounds are mostly re-purposed rounds from other lines. A lot of the rifle rounds are really their V-Max rounds (varmint rounds), and I believe most of the pistol zombie rounds are really their critical defense rounds with green flex tips instead of red flex tips. They're not really any more expensive than their non-zombie counterparts (the .45 ACP Zombie Max is actuall $0.84 cheaper than a box of .45 Crit Defense), and you at least get cool box art....
For example, the Hornady Critical Defense .45 ACP is a 185 grain flex tip bullet, its stats match almost identically to the '.45 Zombie-Max' round...