While searching for where it says that the HD of the created undead has to be equal to that of the corpse (I haven't found that yet, though I found that yes, the polymorphed corpse has no HD, as long as the thing you are polymorphing from doesn't), I found a dysfunction: Animating Zombies and Skeletons doesn't work. You see, Skeleton and Zombie are templates applied to any corporeal creatures with skeletal systems. If I remember correctly, a corpse is defined as an object (Can someone back me up on/disprove this? SRD does not hold anything for me), not a creature. Thus corpses are ineligble for becoming skeletons and zombies.