Every submersible will create a certain amount of heat. It converts electricity into kinetic motion, and every time you convert from one kind of energy to another you lose some energy in the process, generally in the form of heat.

How much heat, that's hard to say. Some pumps are bound to create more heat than others. The average pump probably doesn't generate enough heat to worry about, depending on your reservoir size and how close you are to problem temperatures already.

The only way to know for sure is to test the specific pump in the specific application. Let it sit idle for a couple hours, check temperature, then run it normally for a couple hours and check temperature.