The answer is YES they stack.
When the charm is activated you inflict an elemental or physical damage equivalent to 5% of this creature's life, it means that you are dealing a damage to the creature, so if you have a prey of attack on the same creature it will be applied at the damaged dealed by the charm too. Take a look at the example
Skeleton Elite Warrior has 7800 hit points. He is 0% weak against any kind of damage, except for Holy damage that he is 25% and Death damage which he is imune. So if you apply the charm Wound at this creature, when activated it will deal a physical damage of 5% of his total life, it means a hit of "390", but if you have a prey of attack 10 stars (25% more damage) on the Skeleton Elite Warrior the damage dealed by the charm rise to "487".