I do. But only after I have first searched Company of Men for details on a provider. If I don't find enough detail, I send two or three recent RM reviewers RM messages asking about the guy they have reviewed and whom I'm thinking of hiring.
I keep my requests simple, saying something like "I see you enjoyed your time with ____ last month and I'm thinking of meeting him. I'd be grateful for any details you're willing to share."
I never ask reviewers about rates. I only ask providers directly about rates.
And I find that typically 1 out of 3 RM reviewers respond to me, and I think that's a great response rate. Their responses vary in detail, and some are much more helpful to making my hiring decision than others, but nevertheless I always thank responders for taking the time to help me.
About 1 out of 8 RM reviewers open a more expansive discussion with me.