I'll throw in my few cents here:
In fact, if you read through the battle net site, there are not many unbreakable poison immune there. As long as the poison resistance is less than 110% (I’ll just assume that it is easy to have a lvl7 or above LR after gears), you will break it. With 3 pieces Trang set (preferred glove, belt and shield), you get +2 to curse (help the LR curse), +2 P&B (obviously), and most important, +25% poison damage and -25% poison resist. The only expensive part is the belt. However, I think it would be okay to use the armor (pgems in trade) in the beginning. Here is what I use before I get better gears and it is pretty good, actually.
Helm: +2 necro (or +3 P&B) circle (using Shako now)
Armor: any Vipermage (using Skullder for MF now, Nigma will be great for tele/MF)
Glove: Trang glove:
Belt: Trang belt
Shield: Trang shield with PDiamond (can be socketed with Pfacet once I can up my resist from other sources).
Boot: Aldur boot (nice FRW and fire resist, war traveler if you need MF or any will do).
Weapon: Blackbog’s dagger (nice +PN, and CHEAP, great before you get Death web => the ultimate weapon

)
Ammy: +3 P&B with or without mods (can be gambled or trade with pgems).
Ring: Any will do (+resist, life, if you are rich, you can use Soj or Bk for skills).
Charms: Resistance, Life, Mana as your need. Any necro torch will do (pgems) for its cheap price. Gheed if you are into MF. Anni when you get rich (Um for low one in east ladder). P&B skillers are not necessary but you can add more once you are richer for more damage.
As you can see, you can have lots of +skills for cheap (pgems for most of them). As indicated above, he is famous for its effectiveness in Pits. However, with better gears (deathweb is the most important one), I can do chaos run easily. Even BigD died in few PN with LR on him.
I go the route without any summon as of now. I max all poison skills for sure. Then, I put many points in Dim Vision (lvl22 now with gears). 1 point to bone armor and many in bone walls now. With DV, normal monsters will stand there getting poisoned ? Most monsters will die with 1 or 2 nova even without LR. For tougher monsters (high life, or poison immune), LR is very useful.
Agree with above, I will choose nigma over bramble ?
Cheers!!
Chien