Hammers and scythes actually are in the game - they're tools not weapons though (for BTN and BSM respectively), which is their original use after all (hammers and scythes being used in warfare was mostly due to peasant militias utilizing whatever they had to hand as weapons). So I dare say you probably will never see these as weapons in the game I'm afraid.

Also the way the game's battle system is designed (the Armoury System), your class or Job is your weapon, a different weapon is a different class or Job. So that makes it even less likely you will see alternate weapon types on a specific class.