hotRNA: I believe that most MSTPs (correct me if I'm wrong) are not rolling (OHSU's MD-PhD program is an exception), so they generally will have given out all, or at least the bulk, of their acceptances by their revisit dates. Thus, even though not all of the applicants you meet at revisits will end up attending that particular school, it is probable that those who do wind up going there will have been at the revisit weekend (does that make sense?). So, I think you, in fact, will be able to meet most of your future class at second look...it's just you may not know which they will be. 🙂
Anyway, the main point of the revisit weekend should be for you to learn more about the school and make a good decision as to whether you want to spend 7 or 8 years there. Aside from trying to gauge what your own class will be like, it will also be a chance to get to know current students a little better, visit with faculty you are potentially interested in working with, etc. From the school's perspective, it is definitely a recruiting event.