Does it really matter if radar can see the jumper? First off, who is watching? I doubt ATC is going to track the jumper to the ground. Absent military radar watching the border I doubt anyone would notice.
But let's say someone does notice. Now what? Is there a procedure for ATC, military or anyone else to notify the Border Patrol or anyone else?
A friend of mine who works for the border patrol has a patrol area the size of Rhode Island. Let's say his sector was notified and they told him. If the jumper planned this carefully and had someone waiting to pick him up, then the jumper is long gone before anyone can respond. If it’s a HAHO jump, then the jumper could exit over Mexico and land 25 or more miles into the desert.
All that said, wouldn’t it be easier to get in other ways? This seems like lot's more effort then is warranted for someone to sneak over to pick lettuce. So let's say a spy or a terrorist wants to get in. Wouldn’t it be easier to come in on a pleasure boat, or to drive in from Canada? Jumping will get a single person in but not with any substantial equipment.
It seems to me that if our boarders are so secure that this is what’s needed to penetrate them, then the border patrol, customs and military must be doing one heck of a job! I hope we actually get to this point.