Im sure they do. This happened to me in high school. I had a 3.6 when I applied and was accepted to Michigan State University. Then a week before school was about to start, I received a letter stating that I couldnt attend because of my last semester grades (I got like a 1.8). So im sure they do the same thing in a professional school.
To answer the first question, you must maintain your academics, ie not get any D's after you have been admitted.
To answer your second question, they will not see your summer scores unless you wait until they are on your transcripts that you send to AADSAS, but AADSAS has a point after your application where you can input the grades you recieve during the summer so you should be able to show most of your grades when you first apply and then the summer scores somewhere around October or something like that. So apply early and add the other scores later
I know that once you submit your application you can't change your grades sooo..it'd probably be a bad idea to guess on summer grades. However, in November (through Dec. or maybe January) you can send in any grades you haven't sent in and update your app.
As for the first question, I have no idea..but my guess would be that yes, they would do something like that.