I have had this topic brought up during discussion on Christianity with non believers.. It is actually a common one.
Maybe it is more where you live as the only time I find this topic is on this board or odd places on Youtube. There are many alien cults in the US, last time this topic came up I posted the 'top 10' You do know that the US is the hot spot for alien cults?
If this is a common belief where you are, by all means, incorporate it into witnessing but I have never in my whole 53 years heard preaching incorporate anything about aliens into the gospel message. Only perhaps as a passing joke or in reference to "beam me up Scotty" or some such light-hearted banter.
My experience is that it is evolution that posses a much greater threat, and of course, aliens slide right into evolution because people who believe everything evolved by chance random processes are far more likely to also believe it evolved on other planets as well.
The Bible clearly teaches that demons are real and will try to deceive. The Bible also talks about the Nephilim in Genesis 6 which many like to ignore along with the rest of Genesis, but I see Genesis as being the foundation. It is foundational to many doctrines and Biblical principles including Satan and demons.
People are still driven by the same basic things they always have been; greed and pride. Satan has always used a distorted mirror of what God wants or is or asks for. God said "but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die." So Satan came along and said “You will not surely die,” the serpent told her.
5“For God knows that in the day you eat of it, your eyes will be opened and you will be like God, knowing good and evil.” he distorted what God said.
We then see God bring about animal sacrifice in the Old Testament for sin as a type of shadow of Christ. Meanwhile, Satan had tribes sacrificing people.
Modern man is tempted by the idea of meeting people from other planets and visiting them, why would Satan not take advantage of that? One thing these alien cults share is the belief that one day the aliens will beam them up and take them away. Notice how the idea of being beamed away by aliens parallels the second coming of Christ and the taking away of the church? If God said something one way be sure Satan has his own distorted version of it. Nothing has changed.