At the exit there is a security guard booth with a machine on the wall where you put your entrance ticket into and it displays how much you owe, put your money in the machine and take your ticket back. You have to get out of your car to do this. Then pull up to the gate put your ticket in that machine and the gate opens. Most of the time I pull up and just give the security guard my ticket and they put it in the machine for me and tell me how much I owe and give me my ticket back to open the gate. I'll tip a buck or two for that. The last time we used the garage in Dec the ticket machine was not working and the gate was up and they charged a flat rate of $2 to park.
As for feeling safe in there the answer is yes during the daytime for sure, we have not had a late night in Maho so don't know about that. I would ask the security guard about that. Also all the employees of Sonesta enter and exit by this security booth so there is traffic in this area. At night I would try to park close to the security booth.