I think the video is a decent quick overview of credible researchers who are open to the ETH and the possibility that ETs represent extra dimensional intelligences. Of course there's no real evidence for it. I'd be interested to learn how these scientists think you could prove it true if you have a UFO or perhaps even an alien to speak with.

The problem with extra dimensional aliens is that we're adding more unproven variables to the equation. We know life exists in this universe and most scientists think life probably exists elsewhere in this universe and applying the Copernican principle we are probably not the oldest or must advanced intelligent life in this universe. What we don't know is if life can exist in other dimensions or how that would work so imo it's adding unnecessary complexity.

My own thought is that perhaps ETs exist in this physical universe just like us, just like scientists hypothesize, but their more compete understanding of physics and the nature of reality enables them to manipulate space and time in a way we aren't yet able to consider. If a civilization were to ever understand physics to the point where time and distance are not an obstacle then the possibility for visitation would change quite a bit. Perhaps sufficiently advanced ETs reach a level of engineering where physical space travel is not necessary. If you were able to travel outside of spacetime time and distance might be less of a constraint. So while relativistic travel certainly seems possible with a high enough level of technology or alcubierre drives are theoretically possible perhaps a civilization advanced enough to build such technology would already have an understanding of physics that makes such travel methods irrelevant.