If you are going to dry fire the gun 2 or 3 times on each chamber, then yes fired cases will work adequately. If you intend to pull the trigger much more than this, OKFC45 is correct because the primers will have such a large indentation in them, they would be all but useless. If you intent to dry fire the gun a lot, buy some snap caps as others have said. Supposedly, you can dry fire a Smith with no harm on empty chambers, but again if you are practicing trigger control and intend to do this repeatedly, purchase some snap caps, or keep changing the fired cases every third hit or so.

regards,
chief38