I don't have any information regarding renting 4 wheelers but my guess is no as I have been hanging around this message board for almost a year and haven't seen a thread or any information posted. However, you should rely upon the experts for that type of information.
As far as the map.... http://ambergriscaye.com/pages/town/mapdowntowndetail.html
Try this one. Mata Chica is pretty far above the cut. I've never stayed up there but this should give you a fairly good idea. From what I understand it's pretty difficult to navigate the "road" above the cut so a lot of people use water taxis to travel to town and back.
You might try doing a seach of the messages for "above the cut" or "north end" it is AMAZING what you'll find.