Unfortunately there isn't really a way to check if a character is unarmed in the skill data entries themselves.
There may be a way to script a check if a weapon is equipped, but I can't think of a super simple way to do that.
If you equip a one handed wep and your off hand is empty you get the knockdown ability, so there is a way the engine checks because once you have a weapon on your off hand you get the flurry ability. It may be that you have to add in a knuckles type of weapons or just mod 1h blunt weapons to have no mesh.
