I have fired .38 Super in a .357 Mag. The semi rim of the auto cartridge will headspace the cartdidge in the chamber. If it will chamber, it will fire.
The .38 Super is a semiautomatic pistol cartridge, the .38 Spl is a revolver cartridge. The Super is a little hotter than the Spl, in fact a little hotter than the 9mm.