holy fire does not add damage to anyone but the thing that has it. same with holy shock and freeze. to prove i am correct, go to a game with a char with a holy freeze merc (if you have one) and take note of your melee damage. then walk around letting your merc kill stuff until his aura activates. you will notice that his damage will increase but yours will not

note, i still personally recommend fire golem over clay, but not because of the aura. because of the fact that they have more life, do more damage, and they explode when they are 'born' and when they die