No. Any elemental damage from Zuni boots, a SoJ, a Tal's ammy, or basically any other item has the same effect for a wd. So it doesn't matter if you have +poison, +arcane, +fire, or anything else on your items. Zuni boots only roll with bonus to poison damage, but if they did roll with arcane damage instead it would be no different. A Soj can be arcane, fire, cold, or poison....it's irrelevant. In other words, never pay more for an item just because it adds to poison damage!
Elemental damage on a weapon is different. The damage on a weapon is divided between physical damage and elemental damage (once again, the actual element type doesn't matter, be it fire, arcance, etc). Physical damage is usually called black damage. When people refer to a "black dmg" weapon, it means the weapon does not have any elemental modifier. The Manajuma's Knife always rolls with added poison damage, so it is never a black weapon. All of the elemental bonuses from the items listed above (SoJ, zuni boots, etc) are only applied to the black damage portion of a weapon. This is a bit confusing so I'll give an example.
You are wearing zuni boots (+8 poison dmg), a SoJ (+6 arcane), and a tal's ammy (+6 fire). This gives you a total of +20% elemental damage. Now let's say your MCK has total damage of 1000 - 500 from poison and 500 from physical (black) damage. The 20% elemental bonus is only applied to the physical portion, meaning you'll only actually get a total 10% bonus (because only half the weapon damage is physical). If you were holding the exact same weapon but with black damage you would receive the full 20% bonus.
Hopefully that makes it clear.