I think you are confused about how GPS works.
A group of 24 satellites orbits the earth transmitting the GPS signal. Your antenna can locate your car if it can see at least 4 of the satellites. You location, whether in the boonies or not, is immaterial.
The only 'wireless' part of GPS is that some models use bluetooth, a very short range wireless technology to eliminate the wire you would normally plug into the pc.
An iPad has two ways to find it's location.
1. WiFi iPads look for know WiFi hotspots to try and figure out where they are. This is only semi-accurate and does NOT involve GPS.
2. 3G iPads have a GPS antenna built in. As long as they are in reasonable view of the GPS satellites, the 3G iPad can locate itself quickly and accurately.
Many of the iPad apps out there use maps that are online and require an internet connection. However, some do not. Tom Tom and Destinator load the maps on the iPad and do not require an internet connection. The 3G iPad can connect to cell tower's and get an internet connection if you pay for the monthly service subscription.
The cell network is likely to be the weak link in the boonies but is not an issue if you use one of the apps that loads the maps on the iPad.