Hammerdins are fun to play, all it takes is learning to aim the hammers. The truth is FcR aside, the damage dealt by Blessed Hammer comes from the Concentration Aura being active at the same time. No matter how many points you have in Hammer and it's synergies, without Conc active, your hammer damage takes a nosedive.
That aside, No monster ( except one in act 3, I forget the name & you will likely not cross its path anyway) is immune to hammerdamage. You will own all monsters. You may have problems soloing bosses it you do not have much of a base mana pool, as there may not be any corpses to use Redemption on.
A Hammerdin ...with the right equipement on...is great for Baal Runs, or Pit Runs, either soloing in multi games or in a one player game.
I have one at level 85 right now