Up to AIR 3.3, it was not possible to handle exceptions inside the Cocoatouch Static Library in an ANE. AIR 3.4 onwards, it is possible to use the Objective C @try-@catch-@finally syntax inside one’s native library. The native developer can now also use C++ try-catch blocks successfully. The only thing to keep in mind while using exceptions in native code on iOS is that the exceptions should be handled inside the ANE itself. The AIR runtime will not catch the exceptions thrown by extensions.
You can download the latest AIR SDK with support for handling exceptions in a Native Extension from http://labs.adobe.com/technologies/flashplatformruntimes/