We used to use Vaseline to form a pocket in a ball glove, and the object was not to soften the glove, but to create a hard "pocket" to catch the ball in. Don't use neetsfoot oil on your leather seats, or any other kind of oil. Oil won't evaporate, so you'll be getting it all over your clothes.
The only way to tell if your seats are leather or something else with some of the imitation leathers is to see the back of the leather or whatever.
Most leather car seats from the factory are not 100% leather. The "seating areas", in other words the parts that touch your body like the seat bottom and seat back, are leather, and the rest is matching vinyl.
No one lives forever, the trick is creating something that will.