I keep seeing this theory and while it's not completely out of the question as far as continuity goes, I think it's wrong for two main reasons:
1. The producers said that the skeletons may give insight into the nature of the show and that it will prove that certain things were planned from the beginning. While time travel is certainly an aspect of the show, I wouldn't say that it is the "nature" of the show. I think this line is more directed towards the stones found on one of the bodies: one black, one white. These represent the duality of the universe, something which the show constantly references (faith vs. science, good vs. evil, fate vs. free will, etc.). Having characters we already know would be cool and is probably what will happen, but Rose and Bernard don't seem to be characters whose death would represent a duality, equal but opposite.
2. The biggest support for this theory is that the stones are black and white and so are Rose and Bernard. While this is true, it certainly does not represent anything the show is about. As stated above, the colours of the stones are symbolic of this duality and to have them imply the races of the corpses would cheapen their importance.
I'm not saying that Adam and Eve aren't characters we've seen before, but Rose and Bernard just seem so random for their identities.