I don't have Madden 11 but have had Madden every year, but 08, since EA added the draft classes. So here is my answers to your questions.
1) Just because he goes pro does not mean he will be in the draft class. There will be a cut off. Unless your 80 overall player is in the top 10-20 at his position then he would not show up. I know in years past you would never see a 80ovr player in the class but with the lowered ratings then who knows.
2) Not sure on the cut off. I know with the old rating system I never saw a player rated less then 88ovr in NCAA end up in the Madden draft class. Go to the edit roster menu and change the team to NCAA. Then go to the player in questions position and see if they are in the top 10 overalls for that position. If they are then I would say you will see them make it but if not then they are just not good enough. There is always the CFL or UFL. In years past 85ovr would be way to low but once again with the lower ratings then who knows.
Madden 10 was the first time I didn't use the NCAA draft classes. The preloaded drafts are fun to use. There are some real studs and you can edit the players names so you could make your own draft classes. Well atleast you could in Madden 10.