Someone being sweaty does indeed make them harder. I'm not sure at this point if we are talking about wristlocks from standing or ground. If it's from standing, then what I have found is that grab and lock have to occur at the same time, or else you should move on to something else right away. Don't try to wrestle the wrist. It leads to bad habits.
"Seek not to follow in the footsteps of the men of old; seek what they sought."