The guns a irrelevant in this build as you're not going to kill anyone! Sure, no-one can kill you either :) The only purpose is to potentially kill an NPC to have Determined and Predatory kick in.
Video of build in action http://xboxdvr.com/gamer/sneakystabbalot/video/49669784
And the build in-game http://xboxdvr.com/gamer/sneakystabbalot/screenshot/8792278
My strategy is to run up to the rope (I usually have a single item to 'extract', but in the video I do not) put down the immune box, put down the shock turret between the rope and the other agent, pop survivor link and cut... I also try to cut when there are NPCs around as I can easily tank the NPCs and the victim agent often has to carve up his time between me and the NPCs.
Against a solo player I have had 100% success, against two players I have about 85% success and three players 50% success. Yet to cut a four-person rope!!
Remember, I am solo!
The mods are all ST Health and Turret duration mods - this is mainly for use when I hot-foot it away, I can drop the turret and it lives a little longer to slow down agents running after me. FWIW, I have never been killed running away from the rope cut and running off my rogue status - the health pool is simply too large and the ongoing Nomad heal is incredible.
Talents are Adrenaline (for immunity), Fear tactics (for the turret), Strike back and critical save (just in case!)
One final point, I have two Nomad builds on this guy, the other is a general DPS build running 2xHouse SMGs. I will run around the DZ solo with this build and if I see an extraction I switch to the Dick-Rope-Cutter-Build (I wish we could name our loadouts any way we want!) - what's nice about this is Nomad's Resolve DOES NOT COOLDOWN when you switch between Nomad builds. Anyways, it's a fun build!