"Do vegans realize that they are not saving animals?"
I believe that SOME vegans do realize that they're not actually saving animals.However some believe that their view of what Utopia can be achieved, and that they can save animals. However Utopia, like morals and ethics are a matter of human construct, something which animals don't have. As any form Utopia is of human construct, and is thereby fundamentally flawed, in the fact it as such perfection can NOT be realistically achieved, due to it being of human construct, and everyone has their own view, as to what constitutes that Utopia.
So e vegans may have realized that there are some people who simply can't be healthy on the strict vegetarian, that they follow. Yet others realize whether they want to admit it or not, that some type of hunting at minimum is as -one vegan who was also a biologist many years ago that while he didn't condone it," hunting is a necessary evil." The main point he tried t make, to a much younger vegan, was that it would only take just one animal that one animal that was non native to be introduced into the wild which would be an invasive species, that would upset that balance of nature. Hew was old enough to have learned to temper any idealism, with a sense of reality. Something I hope that the younger vegan, if they're still one, has learned by now, after these many years now gone by.
In the end, any vegan who has a strong sense of reality knows what they're over the long run, won't save the life of a single animal. They realize that what doesn't die at the hands of a human, will die by being killed by another animal. They also realize that they can't save animal if its not born either, as what doesn't come into existence can never be saved, due to that lack of existence.