Well, Rage supposedly stacks with backstabs and guerilla for extra damage
Literally posted in this very thread:
I just tested as a sanity check, and I can confirm this is 100% false. You cannot also crit on a Backstab.
Also, just a reminder that Guerrilla is AP-inefficient. Sneak costs 1 AP to use during combat, so the +50% damage modifier Guerrilla adds is only worth using over a regular attack (costing 1 or 2 AP) if you're entering a fight with a sneak attack, or are using a skill like Snipe or Mortal Blow which already have inherent massive bonuses to damage when sneaking.