Looking at the link you provided, it's very interesting to see how the success rate varies by kickers. Some kickers are obviously much better at the onside kick than others. Better than I would have imagined.
Jeff Wilkins has successfully converted 40% of his attempts, and with 25 attempts, that's enough of a sample size to be taken seriously.
I know I have watched games live where a team has converted 2 in the same game. It's rare, but it happens.
I wonder what is more rare, a successful onside kick, or a QB throwing 7 interceptions in one game?