Anyone tryout a A3 merc using dragon armor, dragon sheild, Hoj weapon?

Thats the same setup my pally is wearing, and I'm thinking of trying it on merc at the same time. Not sure what will happen, but dont want to waste the runes.

Not enough damage from the aura for what you invest into it when compared to other builds.
Remember that the mercenary does not gain any bonus damage from fire resistance, so it's just the base damage from the aura.
They will also not benefit from the aura bonus damage to their weapon since they will not attack with it.
Any other mercenary will benefit more than act 3 mercenary if you want to stick with elemental damage since they will actually attack with their weapon.

What is your paladin built as?

I have a dragondin. Wearing same as above, and flickering flame. I guess also called auradin, but using dual dragon.

Right now I have an A1 Cold Faith Merc. for fanaticism

I would stick to your current mercenary over building Act 3 with holy fire.

never give dream dragons to a merc

no synergies on merc = crap damage