Ryujin
Legend
Well, a poison needle trap would likely make it a skill challenge or encounter, so assume instead that the locks instead are ruined if he fails his Thievery check. After all, I've already stated that if the disease is convoluted or interesting enough to be a skill challenge or encounter then you can't take 10 by RAW.
So what difference does that make, by the RAW, if the lock disintegrated if he failed the Theivery check? A chance for failure or a repercussion for failure are 3e rules for preventing taking 20 and have nothing to do with taking 10.
Except that you're making an assumption about what happens to the poison needle trap that isn't within the mechanics of the trap. Unless there are specific rules that govern what happens to a trap outside of an encounter, I would say that it's a bad assumption.