Quote
She saw the scene in two differing frames. In one, the three men climbed the unremarkable barrier of rough uneven boulders, while in another the telltale marring and scars lingered of enormous energies expended and horrendous damage given and taken. Bodies lay among the rocks – slain Stormriders that she stepped right over. Their armour appeared to be a mixture of their sorcerous scaled ice over mundane materials such as shell, cold-forged copper, and exotic hides. They were fair, with pale hair. The characteristic features she saw among the corpses reminded her of the Tiste Andii.
This seems to suggest to me that Shell can only see the Storm Rider bodies while she's in her warren, Serc. That implies that they are natives of Serc, and that's why their bodies are seen to disappear when they are slain on the wall. Also note that the warren is specifically described as the Warren of Wir and Storm here, where elsewhere it's only described as being the warren of sky. By using the word storm, it seems to suggest why STORM Rider bodies might be seen in Serc.
Also, the comparison to Tiste Andii is interesting, though it could mean nothing. Tiste Sercians?