I did some research on this at one time myself. It's been a while, but IIRC the term "Sneaky Pete" has been used for many years as a general term for anything that's was designed in such a manner as to obscure it's true nature. Also, I think it has been used as a general term to describe something that is concealed on a person, as in a weapon.
I, perhaps like you, was hoping to find that "Sneaky Petes" were named after some 19th century hustler or something, so I was disappointed to find evidence that seemed to suggest the term was simply adopted by the pool world, and was not originally pool-related.
Aaron