just from top of my head.... Hitchens's razor
atheists usually dismiss the idea of God because they want evidence... an atheist that believes in ghost should then apply the same reason to his believe in ghosts
First of all, not all atheists are materialists, so we already know not all atheists accept Hitchen's razor. Second of all Hitchens razor only applies when you're trying to convince the other party, and an atheist materialist who believes in ghosts might not be trying to make an argument for their belief. They could easily say they've experienced something they can't demonstrate, and the weight of their experience is enough reason to convince them.
Not unlike the first people who saw black swans before it was officially documented. They wouldn't have been able to demonstrate their findings, but Hitchens razor would have meant, ultimately dismissing a claim which was valid until evidence could be obtained.
An atheist materialist would respond to requests of evidence with 'I believe it's currently (but not absolutely) beyond our means to obtain evidence, but I have my reasons for believing it to be true.'