[NJump]

My thoughts: Who has a dog in this hunt? Just the coaches. The variables on a coach's evaluation after a game skew any objective report. Strike zone sucked,but he won. Strike zone sucked,but he lost, etc.
For my two cents, use an impartial evaluator. Some one whose opinion can be trusted, who has the knowledge and experience to see the TOTAL performance.
Blew a call? Why? Good/bad position, moving/not while making call, etc. Rules knowledge-- shall we even go there?
Critical question as yet unasked: how much time is a good/bad coach spending during any given game spent "evaluating" the umps.
Personalities-- coach likes to "work" the umps vs. coach who doesn't.
What is the objective of evaluation? If improving the association's the overall performances, only unbiased opinions are worth the paper it's printed on.
Want to find out who is there just for the money? Honest reports will quickly weed those out. Those trying to improve will take evals to heart and strive to improve. End result--everyone wins. Yourmileage may vary.