If Spotify was properly paying its share of royalty fees to the artists I don't think it violates any regulations that they used pirated versions of the music. It's simply more convenient for Spotify because they don't have to rip the music from a CD themselves.

When rights holders use a pirated version of their work it may be embarrassing, but it certainly doesn't violate copyright law. (Assuming the pirates didn't transform the work in a substantive way)