Thing is with Wookiee Rage, given how very difficult it is to avoid taking damage at all in this system, allowing the ability to be applied to the Lightsaber category of weapons means that you're in effect giving lightsabers an almost-always-on bonus to damage, which as noted is something that lightsabers generally don't need given the Breach quality making all but the most obscene of soak values meaningless. Factor in that suffering a critical injury adds another +1 to damage (for a +2 total) and that a number of melee-centric specs offer ranks in Durable to offset the bonus to crit rolls that carrying a crit provides to the attacker, and you could very easily have a Wookiee PC with an "always on" +2 bonus to damage.
So before a GM opts to house-rule Wookiee Rage to work with Lightsabers, they should ask themselves "do I really want to hand out what amounts to a permanent bonus to damage with weapons that already do a lot of damage?"