Silmarillion - Ainulindale

[Aiwendil]

I don't know - I've always seen Tolkien's treatment of evil in his works as rather Augustinian. Augustine wrote in The City of God:

The sins of men and angels do nothing to impede the "great works of the Lord which accomplish His will." For He who by His providence and omnipotence distributes to every one his own portion, is able to make good use not only of the good, but also of the wicked. And thus making a good use of the wicked angel, who, in punishment of his first wicked volition, was doomed to an obduracy that prevents him now from willing any good, why should not God have permitted him to tempt the first man, who had been created upright, that is to say, with a good will?

For who will dare to believe or say that it was not in God's power to prevent both angels and men from sinning? But God preferred to leave this in their power, and thus to show both what evil could be wrought by their pride, and what good by His grace.

This sounds to me rather like Iluvatar's warning to Melkor. Melkor's deeds remain evil - Augustine is emphatically not saying that evil is really good - but Iluvatar in his omnipotence is able to work good by means of them. I don't necessarily see this as implying fatalism or the predestination of Calvin.