Unless the artists self-financed it and didn't make contracts with record labels, it basically is work for hire.
Nope. To be a work for hire it has to either by a work prepared by an employee in the scope of his employment, or it has to be "a work specially ordered or commissioned for use as a contribution to a collective work, as a part of a motion picture or other audiovisual work, as a translation, as a supplementary work, as a compilation, as an instructional text, as a test, as answer material for a test, or as an atlas, if the parties expressly agree in a written instrument signed by them that the work shall be considered a work made for hire. For the purpose of the foregoing sentence, a “supplementary work” is a work prepared for publication as a secondary adjunct to a work by another author for the purpose of introducing, concluding, illustrating, explaining, revising, commenting upon, or assisting in the use of the other work, such as forewords, afterwords, pictorial illustrations, maps, charts, tables, editorial notes, musical arrangements, answer material for tests, bibliographies, appendixes, and indexes, and an “instructional text” is a literary, pictorial, or graphic work prepared for publication and with the purpose of use in systematic instructional activities" (17 USC 101).
Your typical artist is not an employee of the record company and so their work would not fall under the "employee in the scope of his employment" option. That leave the other option. To fall under that option the work must fall under one of the specific categories enumerated in the statute and the contract must state it is a work for hire. Note that is an and, not an or. If the work does not fall into one of the enumerated categories it CANNOT be turned into a work for hire via contract.