re: "Dumb luck"
My point is that ability to survive space travel will never be a trait that is selected for by evolution, because the advantage of the trait disappears in the countless generations that intervene between the rare times that space travel becomes useful to an organism. The "dumb luck" possibility is that traits that had been selected for other reasons also happen to help in space travel during the rare occasion that it becomes necessary.
Of course I could be wrong and Dyson could be right about life living in space vacuum, but that's getting pretty speculative.