A psychic vampire is, in LaVey's use, a person who uses other people's sense of pity to fulfill their wants or needs. By making themselves look pitiful, they arouse other's sense of pity and then they feel obligated to the o-so-pitiful person.
That isn't always the case with those on welfare or government help. Sometimes they are responsible people in the wrong situations. Even though LaVey emphasizes the ego and self-preservation, he does justify being kind and giving to others. On page 51, LaVey's exact words are "If you do something to make someone for whom you care happy, his happiness will give you a sense of gratification." If you do care about wether or not someone is doing poorly, you'll be happier doing something about it. On the other hand, you can just ignore them and not care at all. But it is nice when someone can prove responsibility and use help for a goal to a good life, which isn't parasitic. Psychic vampires are parasitic because that's their lifestyle. They will feed off the help of others until they die or change their ways.
I will point out that LaVey's brand also has Social Darwinism. I usually interpret it as those who are not responsible and self-providing, with future goals and ambitions, will have to either change to compete or become smaller in number. That's their choice, though, and not one I can control. Psychic vampires are probably a great example of this population that becomes smaller. There might be several vampires around at any given point in history, but as long as there are responsible and self-sustaining people, they are insignificant and hold society back, and they will be outcast because others want progression.
So to answer your question, some people do take advantage of the welfare system and are parasitic, but the welfare system is also a way to support those who probably got laid off because less jobs are needed in thier area and it has nothing to do with how responsible that person is, so they need to request extra support to move to a more opportunistic area to find another job. It's a so-so situation. There's some good and some bad to it.