This sounds a bit like the ideas of the Raelians, who are a cultic religion similar to scientology.
The Raelians, like Scientology, mix science fiction with New Age Philosophy and borrowings from popularised and boiled down accounts of Eastern Religions. In a lot of ways for many people, aliens have replaced the Gods or Angels as in our age, science is the dominant paradigm for knowledge and for some people, the objects of science (including speculations about aliens or what they look like) become numinous objects of religious belief.
But, a critique using known facts from astronomy is in my view enough to show the absurdity of any claims that aliens visit or have visited us, tinker with our DNA, or pose as religious figures or ‘Gods’ through history.
There is no scientific evidence that any extra-terrestrial civilisation exists; scientists have searched for evidence of alien life for decades, mostly using radio telescopes to try and pick up signals. No radio signal from an extra-terrestrial civilisation has ever been detected. At the moment our telescopes are not powerful enough to image planets around other stars, but around 220 extra-solar planets have been found, but none resembling Earth directly. No life-bearing planet other than our own is known to exist in the universe.
As for UFOs and accounts of abductions, these have also been scrutinised and in most cases, UFOs can be explained in terms of natural phenomena. Accounts of alien abduction are more complicated and involve psychological factors, but generally there is no solid evidence any human beings are abducted by aliens or experimented on.
As for aliens visiting the Earth in the past and founding ancient civilisations or being ‘Gods’, no archaeologists have found evidence of extra-terrestrial beings in our fossil record, evidence for any advanced civilisations before the existence of humankind in our planet’s 4.6 billion year history, or evidence of any crashed spacecraft. If aliens had visited our planet and wanted to be discovered, surely they would have left behind some artefacts, and artefacts that would have been well protected from the ravages of time yet also not impossible to discover. Arthur C Clarke’s story ‘The Sentinel’, where humans find an alien artefact hidden on the Moon which was left to be found by a newly spacefaring civilisation, is an excellent hypothetical example of this. Yet there is absolutely nothing of that nature which has ever been found; while it is possible we have missed it, it is very unlikely. Clearly then either our solar system has been missed or else an artefact is buried perhaps in another planet such as Mars or Pluto, but I’m inclined to the first explanation.
Another thing is that our solar system is extremely small and insignificant in relation to the galaxy and the overall universe. Most people don’t understand the magnitude of the distances in space. The nearest star is about four light years away. It doesn’t sound like much, but a light year is equal to 9.461 * 10^12 km in distance; that is ten followed by twelve zeroes. In other words, it is 9,460,730,472,580.8 km, or 63,240 Astronomical Units, one AU being equal to the distance between the Earth and the Sun. The nearest star, Alpha Centauri, is 4.2 light years away, or 265608 AU away. The galaxy itself in which our solar system is a member of is about 100,000 light years across and the distance to the centre is about 26,000 light years. The Andromeda galaxy, a nearby galaxy similar to our own, is about 2 million light years away, and the observable universe is about 46.5 billion light years in diameter, measured from any point in space, and is rapidly expanding.
Our planet then is only a tiny speck of dust, a minute atom of creation suspended in an infinite ocean of space. An alien civilisation is extremely unlikely to travel thousands or millions of light years just to harvest DNA and experiment on humans. Perhaps a scientific survey craft might come here, but there are probably billions of Earthlike planets and Moons in the galaxy, if extrapolations on the known numbers of extrasolar planets are reasonable, and there is little reason why aliens would come here, unless they had detected us directly by our radio signals. Even so, I doubt they would come here just to kidnap us for medical experiments or to acquire DNA, as other life in the universe is also likely to be carbon (or perhaps silicon) based, just as we are. Any alien civilisation advanced enough to be capable of interstellar travel would also have advanced biotechnology, and would certainly have no need to ‘harvest’ or use human or animal DNA to complement their own.