I find it rather difficult to view Iago as a victim myself, as whatever wrong was done against him, it is certain that the revenge he achieves is completely disproportionate compared to what happened to him in the first place. Let us remember that Iago tells Roderigo in Act I scene 1 that his chief complaint against Othello, and the reason why he desires to see Othello suffer, is that Othello picked Cassio instead of Iago for promotion. It is the injustice of this promotion, when Cassio is unseasoned in battle and Iago was supported by other nobles, that makes Iago so consumed with the desire for revenge:
He, in good time, must his lieutenant be
And I, God bless the mark, his Moorship's ancient!
Having to serve under Cassio and remain in his current position of power is enough to make Iago angry, and so therefore he could be viewed as a victim. However, it is the extent to which he goes that makes him a definite villain. It is not enough to deliberately cause problems for his master when he marries Desdemona, but he then goes on to deliberately manipulate Othello's weakness of jealousy to drive him to madness to the point where he kills his wife. That is enough to brand him a villain.