I haven't studied these issues in any great detail, and perhaps others have already touched on the same points in this thread, but I'll just try to add my 2 cents.
It's important to distinguish multiple issues that tend to be lumped together:
1. Is there intelligent life in the universe outside the earth?
I see no clear reason why God could not have created life elsewhere (but also no strong reason to think he would have). Some theological puzzles might arise from the existence of extraterrestial creatures, but I don't think they would be unsolvable. And especially if such creatures never come to contact with humans, there's no reason to assume that it would necessarily be mentioned in the Bible.
2. What are the "unidentified flying objects"?
My guess is that the vast majority of such sightings are explicable by more ordinary phenomena (weather balloons, meteors, pranks and hoaxes, etc). I think Dr Hugh Ross also stated that there's a correlation between UFO sightings and the hours of day during which people tend to consume more alcohol. It's also easy to imagine that some secret military technology could be behind some sightings. Even the now well-known F-35 fighters look kind of UFO-like from certain points of view (try Google image search and see if there are pictures that someone could mistake for a UFO in a slightly confused and panicked state). If the US military is currently publicizing reports of "inexplicable" observations, that could easily be a cover to their own secret technology.
3. What's the nature of "alien abduction" experiences?
If some of these encounters are anything other than some kind of delusions, mixing up nightmares with reality, or false memories recovered under hypnosis, I would think the demonic explanation is more likely than "visitors from outer space" explanation. Apparently such encounters often involve a clearly anti-Christian message being promoted by the alien beings. Also if Dr Hugh Ross is correct, there is a strong correlation between occultic practices and such experiences.