React Native is supported out of the box. Just make sure to import everything from "mobx-react/native". Remember to slice() / toJS() before passing them to built-in components and you should be good to go.
If you want to use decorators, remember to enable them in .bablerc (I saw there is also a preset for that in RN: "presets": ["stage-2", "react-native-stage-0/decorator-support"])