Not really. They can be, and many are, but they do not have to be.
Most of my RAW files are kept in 16 bit mode throughout the processing, as PSD files. When I am finished I save them as PSD. Most never go to JPG unless I am converting them for web use (actually most never go to JPG at all because I shoot RAW with small JPG so I have a JPG to email).
As I understand it the printer driver may convert the 16 bit files to 8 bit, but it is not jpg. Some printers may use a 16 bit file directly.
Of course my cameras only capture a 12 bit file so the 16 bit file is probably padded with four zeros for the MSBs.
boB