I know there have been a zillion questions on Slashing Grace, but I haven't found this particular instance asked.
If a Golemfist Magus has the Sharpened Arm arcana:
(Sharpened Arm (Ex): A golemfist can rework his arm to more closely resemble a blade. He can choose to deal piercing or slashing damage with his golem arm. When he does so, the golem arm threatens a critical hit on 19–20. The artificer also adds keen and wounding to his list of arcane pool weapon abilities)
Can they use Slashing Grace with it?
Slashing Grace: Choose one kind of light or one-handed slashing weapon (such as the longsword). When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon (such as a swashbuckler’s or a duelist’s precise strike) and you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The weapon must be one appropriate for your size.
I know it won't work for spell combat, but for general attacks: An unarmed strike is light and a sharpened arm can do slashing damage, so there is a colorable argument that a sharpened golemfist arm is a light slashing weapon.
