I think it is extremely improbable, and that the idea is bordering on pseudoscience. As I have said before, the logical difficulty with all such hypotheses is that the extra-terrestrial visitors themselves must have evolved from simpler forms of life. Either this simpler life got started somehow on the visitors' planet, or a previous generation of alien visitors started life on 'our' visitors' planet.
The first hypothesis merely moves the problem of abiogenesis to a different planet without solving it; the second leads to the same problem of the origin of the previous generation of alien visitors. This leads to an infinite regress, like the old question of 'who made God?'.
While I find it mentally staggering, God always was and is. And always will be. I know by logic that humans were not *always here.* I don't really need proof because my mind and logic tells me that humans, like dogs and cats, had a beginning to their existence. Oh yes, also the Bible tells me humans had a beginning, they (we) weren't "always here..." Please don't get me wrong -- I am not likening humans to dogs and cats, just to the logic of their existence. I also believe "I" wasn't here (around) before I was formed by physical means between two people in my mother's womb. I do not believe the stories others may tell about souls injecting into bodies, as if they may transfer from animal to human and so forth.
So we all have beliefs, some based on logic, some based on belief. I used to work for a publishing house that published stories by scientists whom I guess enjoyed writing science fiction as a hobby. That was when I was young and not into things like that, meaning I didn't care or question what a scientist might believe or imagine. But now it makes more sense that a scientist might desire to write sci-fi based on what is not known*.
Take care, nice talking with you a little bit.
*not that I would agree...now...