User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4649443-20121109220822/@comment-5112532-20121111114921

The relevance of Percy and Jason fighting in TMoA was that it was an actual scene from the book.

I think it was also to increase speculation and excitement about the book before it came out because readers know that they are on the same side. And the owl in the sky looks like a godly presence, which kinda should be Gaea who incited Percy and Jason's fight via the eidolons, although the owl obviously stands for Athena and her Mark...

RR and John Rocco are not going to have a book cover that doesn't relate to the book, all book covers usually have some relation to a scene, theme or character, etc. in said book.

So unless Hazel and Frank end up at CHB (which I don't think they will) and splash through the creek, then it probably won't be on the cover for House of Hades..!