This is an interesting question and one that can be anachronistic to some degree. You have to realize that in the ancient world whatever the gods did was beyond human judgment. With that said, there is nothing in Oedipus that would suggest that the gods were evil. Just because there was a prophecy that Oedipus would marry his mother and kill his father did not necessary make the gods responsible. To argue that some sort of predetermination makes the gods liable is to think too rationalistically.
If there is anyone to blame, it is probably Oedipus. He is the one who is characterized by hubris (pride). He is the one who thinks he is so wise and the one who can solve all problems. His pride drives the play and in the end, he is punished. In other words, he transgressed human boundaries. Keep in mind that there were two basic axioms in Greek culture: (1) know yourself (that you are not a god), (2) nothing excess (do not transgress what is human).