If you put a creeper and a dragon in a battle ring together, raising the creepers health to the same as the Dragon's with no source of regeneration, the Dragon would most likely win if you think about it! =D
So the dragon would be aggressive towards the creeper and attack, and the Creepers first reaction would be to stand still. With the raise of the Creepers health the creeper would not die, but suffer the damage. Now the creeper is aggressive toward the EnderDragon. The creeper would get neat the dragon he would explode, attacking.
So the creeper has made the dragon suffer slight damage, but the creeper died, as in exploding. Or at least that is my guess is how it would go down. =)