There was once a dispute on the Thalion Webshrine about music. In regards to the CD "Give it a Try" by Jochen Hippel. A few sharp emails and I never heard from them again.
Ask them to provide a copy of the employment contract between the company and the musician where it states that any music created by the artist during their employment remains the copyright of the company.
Very few musicians sign up to a contract like this. Even in the games industry. It's only if they were full time employees. Most musicians in the games industry are freelance and work for many companies at once and almost always retain copyright.
If they cannot produce the work contract signed by the musician (which I would imagine very few companies could from back then as they have all been thrown away by now) then chances are the musician can claim ownership and thus grant you publication rights.