Yes - as heat, but, unlike in the case of airplanes, remote detection of submarines by infra-red is only possible insofar as the surface water temperature is increased, as infra-red is just another form of EM that is strongly attenuated in water.
Nevertheless, I believe the detection of submarines by their heat output is being used. One thing I had not thought of until writing this reply is that, so long as this method is inefficient, a submarine propelled by this method will require a larger powerplant, with a correspondingly larger heat output (and noise output from pumps, etc.) than comparable submarines driven by propellers.
Quoting the press release: "<...> could potentially yield 90% efficiency in a magnetohydrodynamic drive, which is worth pursuing". That's close to the efficiency of electric motor, which means the new drive will need roughly the same amount of power, as the existing ones.
Nevertheless, I believe the detection of submarines by their heat output is being used. One thing I had not thought of until writing this reply is that, so long as this method is inefficient, a submarine propelled by this method will require a larger powerplant, with a correspondingly larger heat output (and noise output from pumps, etc.) than comparable submarines driven by propellers.