Wanting communication with competitor before they hire ex employee - is this letter ok?

Well, my best advice would be to have a lawyer review that instead of Yahoo Answers. Saying ANYTHING about an ex-employee when you haven't been asked can be construed as harment, and you could be opening yourself up to a lawsuit. In some places, the only information an ex-employer is legally allowed to provide is the person's dates of employment and position title - and that only if asked.