I think it'll be left somewhat ambiguous, but I see the conflict of Ice and Fire that Melisandre sees as so relevant to the grand scheme of the series that it can't all be bullshit.
Well, it's clearly not ALL bullshit because we have seen quite a bit of both ice magic and fire magic in the series, so we know that certainly there is power in both. What I see as bullshit is Melisandre's assertion that fire is "good" and ice is "bad," and things will be all right once the good guys (R'hllor followers) beat the bad guys (Others). I think the endgame will be considerably more morally complex than that if the rest of the series has taught me anything.
If Jon truly is the Prince That Was Promised, I think the fact that he's equal parts Targaryen and Stark is a significant hint that one side is not morally superior to the other.
There has to be some explanation for resurrecting Dondarrion and Cat, for one thing, which at present only R'hllor offers.
There's certainly fire magic that can bring people back to life, but I see no evidence that there's a sentient being who actually cares about the affairs of humans behind it.
And the conflict of fire and ice, well, it's kinda in the title!
Though I think the title holds more than one meaning (as GRRM titles often do), I think A Clash of Kings heavily hints that the primary meaning is that the "song of ice and fire" is the song or story of a person who has elements of both, which Rhaegar believed at the time to be Aegon but is probably Jon Snow.