Maybe I've overblown the similarity in my mind, but I find it interesting that both have strong apocalyptic elements about world-ending battle and the devouring of the heavens, etc. Was this noted by people at the time? I would think missionaries could draw on the common themes to help spread Christianity. Or was the story of Ragnarok affected by the introduction of Christian apocalyptic literature?
As a side question, how common is apocalyptic literature, across cultures?
Unfortunately, the accounts we have about Ragnarok (eg, the poetic Edda) were written several hundred years after Scandinavia's conversion to Christianity. This makes the untangling of the Christian and pre-Christian elements very difficult, because we don't have a pre-conversion Ragnarok story to use as a baseline for comparison. And we can't assume that all the bits of the Ragnarok stories which differ from Revelation (and other Christian apocalyptic texts) weren't changed in unknown, untraceable ways by the Christians who told them for generations before finally writing them down.
I realize this is not the answer you were hoping for, but the difficulties of the sources make pre-Christian Scandinavian religion a very difficult topic to talk about with any kind of certainty.