An Atheist is one who don't believe in the presence of God, As they don't believe in God they do not have a worshiping place or a religious text. Where as a Raja Yogi who practices Raja yoga meditation becomes a Devatha during Sathya yug and Thretha yug. Their they do not know God, they don't have a worshiping place or a religious text. This is the similarity between people who follow Santhana Dharma and Atheist.
Another similarity is that the Devatha lived happily in Sathya yug and Thretha yug, that is why it is called heaven on Earth.
In Kaliyug, the country where the happiness index is more is in the countries where the Atheist are in large numbers.
This is the similarity between Sanathana Dharma and Atheist, even though they have a basic difference, the Devathas became Devathas because they believed in God in Sangamayuga. Where as Atheist don't believe in God.