I thought that a great idea... and playtesting proves it. once you get your sneaking to 5 (so it only takes 1ap to sneak), you can usually get two ranged sneak attacks per turn, for an investment of relatively few points, since there is sneak on a lot of items, plus void essence. really only need to invest about 3 skill points, take the guerilla trait, and voila, stealth archer.
Assuming that Guerilla damage is additive
which it is not and not multiplicative and your archer is attacking with a Bow, Guerrilla only adds a minimal damage boost per AP:
base dmg 100 +15 leadership +100 Tenebrium skill +50 Oath of Destruction/Bully = 265 dmg for 3 AP or 88/AP
base dmg 100 +15 leadership +100 Tenebrium skill +50 Oath of Destruction/Bully +100 Guerrilla =365 dmg for 4 AP or 91/AP
