Yes, they can unpack the apk and see the resources. The code would be more difficult, but still possible. See apk-tool for more info.
To continue this conversation to it’s next logical step, I present this point: Every developer needs to understand there is a certain amount of risk involved when bringing something to market. Beta testing, impression requests and constructive feedback are all necessary when producing a worthwhile app. At any of these stages, someone might steal your idea, resources, theories, code methods etc. This is a reality of which every developer needs to be aware.
What cannot be stolen, however, is your drive and determination to make something interesting that people want to buy. Piracy, IP fraud, misappropriation of assets or any infringements against your product can be and are very frustrating. Even when someone copies your app wholesale, it should serve more to encourage than deter. Your resolve should be bolstered by the knowledge that your idea was good enough to steal (see Temple Run and it’s millions of clones).
I’m not saying it’s OK to let people steal from you. By all means, protect your investment. But there is no perfect solution to keep individuals inclined towards immoral activities from stealing from you. Your best defense is to keep innovating and ensuring your products include your own uniqueness and potential, which no one can ever duplicate.