You can substitute the two and the olive oil is healthier yet you will NOT have the same results.
Oil has a low and narrow melting point - shortening has a higher and wider melting point. With oil the fat melts at a low temperature, the batter spreads more, becomes thinner, and allows moisture to escape before the dough is set by the temperature - resulting in a crisper bread. Because of the higher melting point of shortening, the corn bread doesn't spread as much, and the dough sets before as much of the moisture has a chance to escape - resulting in thicker and moister bread.
Shortening also contains something that butter and oil don't - air bubbles which expand when heated. You can overcome this to a certain degree by "creaming" the sugar and oil together. This incorporates air into the fat.