On the topic of hand-to-hand, it's an extra skill like Katanas, so I don't see why there can't be unarmed weapons. In fact, I had planned for Kouki to be an unarmed fighter and for Rikuto to give him a cestus for Christmas, but I guess I should have asked more about that first.
Well, apart from all of the known arts for Martial Arts being unarmed (which, technically speaking, could mean absolutely nothing), there's the fact that martial arts weapons are never seen in either the anime or the LN.
Now, it's not all too likely that there are no Unarmed weapons, and there's nothing to suggest that there aren't. Kirito never uses any of them, though that may largely be due to the fact that he's mainly a swordsman.
We could take this the other way as well. Given that it's named "Martial Arts" and not "Hand-to-Hand", the skill may well use the feet as well, and because of this, the damage calculation may not take weapons into consideration, but instead it would look at Attack, Defense (Provided by gloves/footwear), Speed, and Skill Level.
I've actually been thinking about this skill a lot, because this is one of the skills I'd originally planned for Godot to have (though, seeing as we hadn't gone past the first floor in the first month, that was impossible). Really, it could go either way the way I see it. Since the skill itself isn't all too elaborated on, it's completely up to the GMs (well, it'd be up to them anyway since this is non-canon).
