Agree with rijaljun, brand Ambassador don't need to a celebrities. Some project more prefer if their ambassador have deep knowledge in blockchain technology and the project detail.
That's why the Ambassador usually is someone from their community that already join for certain period and follow the project development.
If someone can promote their projects through world popular celebrities then it would also good, not sure which one is better. By paying celebrities, no need to spread the business per country or area but the whole world at once. Unfortunately, there is no new project that willing to pay celebrity, cause they are not even sure with their own project.