In the talks I've heard astronomers give, the life they expect to find in the universe is viruses, not sentient life and not similar to humans. I haven't heard anyone say it's "reasonable" to think there could be other intelligent/sentient life somewhere similar to humans.
In answer to your question about "Would they be atheists?", since we know nothing about how God has revealed Himself to them, we would have to make assumptions from what we know about God.
- Since God created them, He would love them just as He loves us, whom He also created.
- Since God loves them, He would be interested in a love relationship with them just as He desires with us.
- Since God desires to be in a love relationship with them, He would reveal Himself to them in some appropriate ways.
- Since God would have revealed Himself to them, they would have the choice to be God-lovers or atheists, just as we do.