In way of disclosure, I am a program coordinator.
It wouldn't really matter if the SFMatch receives a Dean's letter early - they are not allowed to release them to the programs (in my understanding of the process) until November 1.
Usually we hold all our interviews after Nov. 1 so that the Dean's letters are in the file by the time of interviews, and if we have to interview prior to receiving those we do still review them before ranking, for sure. Our Chair and PD read them carefully, and often there will be M3 core clerkship and M4 ophthalmology rotation grades and comments included on the Dean's letter which did not get included on your transcripts, especially if you sent your application in fairly early.
Dean's letters also will note if you have been selected for AOA, which also sometimes occurs after you have submitted your initial application, as well as some of the other statistical information someone else mentioned above.