I think it's quite appropriate to have your T speak with the psychiatrist beforehand if all parties, ie, your T, your doc and you, are all comfortable with this. I have done this myself, primarily because I was extremely reluctant to engage with the doc at the time and was finding the prospect of having to tell my story from scratch to be extremely distressing... not saying that it's necessarily the right or wrong approach, but having someone else who knows you well paint a concise, instructive and up-to-date picture of your situation can cut down on the info gathering time taken at the beginning and can help to establish the relationship with the doc, at least to some small extent.
Every psychiatrist, like every T, is different in their approach, style etc. I have found sessions to be conducted much more from a talk-based, rather than a medical perspective. I have deliberatly avoided use of the term "therapeutic", as I've found that most of the talking tends to be done by me, and the psychiatrist has always tended to adopt a much more passive role than that of my T.
Personally I haven't found psychiatrists' intervention to be very helpful at all, and I have seen 3 of them in the past 18 months. Then again, I have an excellent T who has a stranglehold on my therapeutic needs right now, and I am currently medication free, so in some ways my need for a psychiatrist would be questionable.
Really hope you manage to fluke a good one - I'm sure they're out there!
Maddog