I look at the rules and see "makes a Brawl check to deal damage to an opponent."
But then we are back to cherry-picking. The rule for Trandoshan claws does not stop at "+1 damage". It also sets a static crit value. It does not say use whichever part(s) you want. And it doesn't say ignore some of it if you want.
So if you are a RAW purist, I don't see how you can then allow a Trandoshan making a brawl check (of any kind) to have any crit value other than 3. Heck, the rule for their claws doesn't even say you may use them. By RAW you must use them all the time .