Yes, Google's decision to stop censoring results in China is justified, because Google's decision resulted in a more free and more fair internet. Even though Google's actions in regards to email monitoring are somewhat questionable, Google is helping China progress into the modern era by allowing people in China to have open access to the internet. Even if they are hypocritical, the result is admirable.
Google's decision to stop censoring search results in China is generally a sound one, and the context of email hacking does not make this any different. Even though some governments such as China want to keep certain information from their people, the Internet is global and not under one country's jurisdiction.