Yes and no. As others have noted in this thread, there's a strong element of, "The end justifies the means," in many plot situations. The "Unforgivable Curses," for example, become, not "forgivable," but not even worthy of mention, when performed by a "good" character.
It's true that it's a desperate struggle for survival, where moral confusion is more likely than not. I'd hesitate, however, to describe any character overall as "doing Christianity."
Well, no -- it would have been contrived and boring to make them perfect little doers of the Word. They've all got flaws that they have to overcome, and like any real person they fail a lot. But again, look what sorts of things they do stand for. It reminds me of this:
Then the righteous will answer him, saying, 'Lord, when did we see you hungry and feed you, or thirsty and give you drink? And when did we see you a stranger and welcome you, or naked and clothe you? And when did we see you sick or in prison and visit you?' And the King will answer them, 'Truly, I say to you, as you did it to one of the least of these my brothers, you did it to me.' (Matt. 25:37-40)
One of the big reasons that Harry triumphs over evil is because he's like this -- with house elves, goblins, centaurs, and so on. I'm also reminded of Paul's exhortation to Philemon, urging him to see his slave Onesimus as more than just a slave, but as a brother in the flesh of the Lord.