Yes. The relay would complete the circuit to ground for defogger and remain energized as long as the engine is running.
If you want to turn off the defogger how is that controlled? Is that also on the negative side? If so you won't be able turn it off.
Also, how is the temperature controlled? You don't want to by-pass that or any other safety overheat if any.
What make, model and year is the car? And let's see a copy of the instructions for the remote instead of guessing.