Need to add support for Creeper and Steve heads as drops. I didnt see it in the list in

http://jd.bukkit.org/apidocs/org/bukkit/entity/EntityType.html

Could this be done?

It's actually a material and not an entity. Look here instead:

http://jd.bukkit.org/apidocs/org/bukkit/Material.html

For the different types of "skulls", you'll need to add a data value at the end of the item. Here's an example with data value set to 2:

Creeper:
  Drops:
  - 'skull item.2:1-1:100'

I don't have a good reference/link for the data IDs so you'll have to experiment.