Is dishwasher salt the same as swimming pool salt?

NO -------

Dishwasher salt is, however, the same as softener salt as used in water softeners for houses. You could use granular or tablet form. It's approximately one third to one quarter of the price per pound /kilo. You may be causing more harm to the pool & equipment by using other type salt. The savings from the wrong salt could result in replacing major components of the pool system. Not a good idea. Use what is recommended - there is a reason for those recommendations.