Not necessarily. Watermarking an audio stream like this wouldn't require that high of a bit rate. It could easily be hidden "under" the content using coding techniques like direct-sequence spread spectrum.

A real world example is GPS, which uses a spreading code to provide about 30 dB of gain. GPS signals aren't directly observable relative to the noise floor in many receivers. It's not until after the signal is "de-spread" that it becomes observable in a spectrogram. This process requires prior knowledge of the signal structure.

In short, if you don't need to send data at high rate there are many ways to hide your signal.