My impression was that the "ghost" comes less from the formal NDA and more from the fact that somebody else produces/writes the work and is uncredited for doing so. Then, the "author"/"producer" passes it off as their own work.

Yeah that's both true and the fact that it is a work for hire where the agreement implies the original author cannot claim credit, hence, turn into a ghost.

I think the difference here is that the AI isn't a "work for hire" setup, it's more like a tool. It would be closer to buying algo sample packs, using Apple's Logic Pro AI drummer for part of the work, or other drum machines for example, and working your way around to glue them together into a composition.

The parallel would need to be between "tool" <—> "composition", rather than "author" <—> "composition" imo.