Interesting thought, but I hate to say that I have a way to disprove it.

Dumbledore probably hired Snape because no one else would ever take the job since it's obvious that you'll get killed or something bad will happen to you. And Snape's been wanting that job forever because when it talks about him as a student at Hogwarts, it says that he was REALLY good at Defense Against the Dark Arts. And later on, we know that when he grew up he used what he knew about the subject to work for Voldemort because he's a fru-monkey like that. You get what I'm saying?