I seriously doubt they are "stolen," being that there would be hefty lawsuits accompanying them.
In the episodes "Krabs Vs. Plankton" and "Driven to Tears," the theme to "The People's Court" plays. Would they have to get the copyright permission? (or whatever they call it.) Probably not; "The People's Court" theme is so well known that if anything, it would give that particular show even more visibility, like advertisements.