It isn't important to the general definition whether a specific instance of a painting or novel is being observed. If you're asking whether theme would still be a meaningful concept if there were no humans in the universe, yes it would. It would be described in terms of hypothetical creatures called humans and the way they would express their thoughts and emotions with language, if they existed. On the other hand, "qualia" is not a meaningful conept in a universe without experiencers, because to know what a qualia is is to experience it.
Well of course they are. We experience what is in our brain. The question is how are they aspects of that thing, and what it is. The claim physicalists make is that they are the same thing looked at the same way, and that to explain how neurons work is
to explain experience.