Spun the engine backwards!?

C'mon.
Using the ebrake is a technique used in rally driving to get the rear to slide out giving you a straighter shot out of the turn.
However, that is a driving technique with no reason to go 360 degrees.
Doing a 360 (full spin), in a parking lot I hope, is much easier to initiate with the ebrake, then by cutting the wheel and applying power. Depending on how fast you're going cutting the wheel won't necessarily give you a 360.
Doing a complete 360 is purely a stunt but it will give you a sense of what it feels like to lose control completely. Thus, doing this in a safe empty parking lot could help your overal driving skills. Knowing how a skid feels and how to potentially control it is an important skill to have.
Once you disengage the DSC, keep holding the button and you will see the "brake" light come on as well. The dealer tech told you a sensor went "out"? Meaning, it fried? If so, then you don't have a problem. A sensor died, so be it. Replace it and move on.
TT