Regardless of what they believe in their private lives once they wear their scientist hats scientists work with the principle that all phenomena have natural causes. Besides scientists are kept in check because their works are peer reviewed.
In other words, works of an atheist scientist is reviewed by her peers, including those who are theists, and vice versa.
Furthermore scientists do not work in a vacuum. Russian or Chinese scientists review works of their peers, including those from the US and Europe and vice versa.
In summary, science is built on the contributions of scientists, not on their authority. Religion, Politics, or Nationalism, by design, cannot mix with science.
Trivia: Worldwide there are more theist scientists and than atheist ones.