While some used to see extraterrestrial life something foreign and dangerous, that’s not quite the case today. People feared the idea of unknown entities but with the worlds knowledge of science and astronomy continuing to evolve, so too does human understanding. While there’s still fear that it’s outshined the curiosity of these unknown and mysterious beings.
Religion did not account for the sciences to discover ideas such as life outside of earth or evolution but has adapted to fit with the era. That’s not to say that religion has fundamentally changed what it is or stands for, but that it has been looked at with new eyes to determine its meaning. 
Depending on a person's faith and religion, it might affect how they view alien life and whether they exist.
What it boils down to though is not if alien life exists for humanity to discover or convert; it’s if humanity is ready for aliens.
People like Giordano Bruno have died for their own beliefs, and in the past, it’s quite easy to say that the revelations of today would’ve never been accepted as truth. Humans don’t know if aliens exist, but their existence would not necessarily derail their faith.