Background-wise, the Night Lords specialize in terror tactics, lightning raids, and stealth- committing only when the enemy is at their most vulnerable. They mostly just disdain most of the other Traitor Legions, especially among the less Chaos-corrupted Night Lords. They almost never deal in summoning daemons, though there are several Possessed/Daemon Prince Night Lords. Daemon Engines might be another grey area, as those are essentially weapons (plus this gives you an excuse to take a Heldrake). Raptors are kind of their signature unit.
Re: using Crimson Slaughter rules: all your units causing Fear is certainly fluffy, as are the more defensive/'stealthy' Possessed, though you lose out VotLW, so it depends on which you prize more in terms of background. I'm not super hip on 30k, but Raven Guard seem like a good substitute.
Makes me pine for the 3.5 'dex and its legion-specific rules, when they all had Infiltrate and Night Vision.