For those fallen angelic beings to be responsible, over the long centuries, for using their powers to dupe men on this Earth into believing that there are alien races from other planets appearing on and around this earth would not be inconceivable at all.
I believe Scripture would easily allude to the above.
Please re-read my post— I said that I was surprised that believing Christians would DOGMATICALY believe this- e.g. state this as a position of formal Christian doctrine. I personally do believe that aliens are demonic manisfestations for a number of reasons including some Scriptural support; however, I would never state that this is a dogmatic part of Christian theology or cast stones at those who believe otherwise.