Yes, anyone can enter the gates of Sandestin. Just tell them where you are going, once inside, eg- "I'm going to Baytowne." The point of the guard gate? Who knows. Maybe intimidation, but more likely to keep people out of areas in which they shouldn't be. When you go to Baytowne, you get a particular color parking slip which you are to display. If you have a Baytowne parking slip, security can easily spot you in other areas.
If your friends want to see you, they simply say they are going to your address.