The remorhaz page gives you the relationship to frost worms as part of a “Related Creatures” sidebar, while the frost worm only has “Additional Lore”. I assume this means that the two are related, but no one in universe actually knows for sure, since the remorhaz takes centuries to metamorph into the frost worm. Looking at the Pathfinder Wiki, I can’t find much more that goes into the details of either creature.