Actually, simple hooks attached to the forearm with leather straps are among the earliest of functional prosthetic devices, and certainly would have been more usable than simple pegs. Although some surgeons did develop "fancier" prostheses (e.g. Paré), these would have been too expensive for most amputees, and probably would not have served well in the rigors of shipboard life. Hooks are well-documented in any books on the development of prostheses, and it is fairly well-documented that some sailors/privateers/pirates did make use of them. How many people used them in "pirating" is certainly not known, but there are repeated examples referred to dating from as early as the 1500s.