I had the same question a while back.
I don't think they can see anything until its in the ERAS postoffice.
I don't think it matters too much this early, either. The early bird programs are just now putting out interview invitations, as it appears to me and my friends. So I think you'll be fine. Programs download often for the most part, so they'll get your letters. They do have to download your MSPE in November, anyway.
Interestingly, I've gotten a couple of invites from both competitive and less competitive programs. My application is not complete, only 2 of my 4 letters are in. Also, I'm waiting on my step 2 scores. Probably my very good step 1 accounts for the invites? I don't know. I had assumed only non competitive programs would issue early interview invitations for people with incomplete applications, but this is not the case. Seems each program goes at their own pace to me. I'm an IMG - I think most of the people listing tons of invites right now are U.S. students, and have more complete applications a lot of the time.
Anyway, hope that helps a little.