Hate to bump an almost 7 year old thread but I was wondering the same thing myself and couldn't dig any information up.

I have the USAA Amex and just used their concierge service to book a really hard to get restaurant for a upcoming trip to Paris. The women was helpful, took all my information down, and told me I would be updated when they attempted to call and book (as they had to call during opening hours).

Got a email the next morning that my reservation had been confirmed. We'll see when I follow through and go next week but so far so good! Would definitely use them again! Just posting for anyone coming across this thread like I did when I was searching for info.