At this line: https://github.com/coolAlias/ZeldaSwordSkills/blob/1.8/src/main/java/zeldaswordskills/block/tileentity/TileEntityPedestal.java#L110

Behold, the mighty stone shovel!

Any item marked as a sword in the WeaponRegistry will function in the pedestal. Non-sword weapons and other items not allowed because it's a sword pedestal, but there's not really any other reason to disallow them.