I'm a NOT China developer. Why do I need to fill in the China Tax Form? Do I need a Chinese address and/or company in order to do this? What do I need to fill in in the China Tax Form section?

Since your content is/will be published in China, a China Tax Form is required. And it will provide to China government.

All the China earnings will be transferred to you from China. 

Regarding the China Tax Form, you don't have to fill in the Chinese name and address. Instead you can type your company name and location in English and you can check the “I am requesting VIVEPORT translation services” box. We'll help you with the translation.

Question? Please contact us at https://developer.viveport.com/contactus and we’ll assist you in resolving the issues.