The hight/weight restrictions are removed for athletes. however, they still stand when the player graduates.
For Navy, if you are 6' 6" and over 230lbs you can't be admitted into the Academy as a normal student. If you are over 300lb's they won't look at you as a football recruit. Once a players eligibility is gone, the standard height/weight restrictions fall into place and a player must meet those guidelines.
Since this limits who Navy can recruit, The coaches have to work harder to but players on the field. IMHO, the Service Academy coaches are some of the best. They don't get the recognition they deserve.