Well, not quite. If you dump the ROM of a game cartridge you have purchased and use that dumped rom to play your game that's legal. If you pirate the ROM, that's still illegal regardless whether you own the original game, however the end result is identical and there's really not many ways to prove you didn't dump your own roms.

Unless, of course, you don't own a rom dumper and have an internet history of visiting rom sites. Even then it's technically circumstantial evidence.