You can but it won`t save your game.
You might have to start over most of the time.
It happens to me on my Japanese Leaf Green and Ruby version.
Though it is awesome to have Japan games I don`t think you can actually play the game on an american console.
I have no clue for sure,since I don`t have a japanese game,maybe its just my cartridge,but I insist that you`ll need a japanese console in order to save.
Other than that,yes,you can play Japanese Leaf Green and Ruby on an American DS as far as I know.
If you need anything else just visit me on DeviantART.
I`m always online. http://deathwolfblood.deviantart.com/