This is a sophisticated question. Of course, Oedipus can be guilty and innocent at the same time. In fact, all people are innocent and guilty to some degree.
When we look at the life of Oedipus, we see that he is guilty of certain things outright, such as his hubris. This is to say that he takes himself too seriously and he thinks that he could solve any problem. Moreover, when he is confronted by the fact that he could be the source of the plague at Thebes, he does not even consider this fact, until he is forced to. In this sense, he is guilty of pride, which was a huge transgression in the Greek world.
In some sense he is also innocent. It is true that he unwittingly married his mother and killed his father. There is guilt in this, but his guilt could have been much greater, had he done these things on purpose! Oedipus at Colonus redeems Oedipus somewhat. He becomes a holy man in sense and be becomes a blessing to Athens.