I would question the idea of having knives as a very integrated part of this "disguised" martial art. At least in the begining of it, since knives are a very offensive thing. I mean, a kitchen knife, probably yes, or maybe a knife for a favorite servent or one entrusted with some important position. But your average slave?
Now, on the other hand, there are lots of things that are knife like, or can be made knife like, and don't have the same negative reaction from the slave owners point of view as a knife. Like hand shovels. No one looks at a hand shovel and thinks, "Hey, that could take my throat out." But it can be sharpened, and shined up so that if someone was dancing with a pair of them, it might just look pretty. Anyway, just my rambling on the subject.
Though I do wonder if there would have been some group of slaves in a mine who created a martial art with pick axes.