Landscape Mobile is intended as a navigational aid and data gathering tool. When determining whether an encroachment exists, observations made with the maps on Landscape Mobile should always be confirmed with secondary evidence (physical boundary marker recovery or a professional survey).
There are many GPS receivers on the market that communicate with your phone or other mobile device through a Bluetooth connection. In most cases the manufacturers of these devices have made them in such a way that their GPS location data is sent through the standard operating system services so that any app running on the device has access to it.
Landscape uses the GPS data the system sends to it without knowing where it came from. It could be from the built-in GPS or an external GPS connected via Bluetooth. To Landscape it is all the same.
However, many high-precision GPS devices only communicate their actual accuracy readings in a way that doesn't get passed on to Landscape. So, although you may be getting the high-precision latitude and longitude readings from your device, the reported accuracy may be 20 meters instead of the 1-meter, or less, accuracy you were expecting. Nevertheless, the actual location data is going to be the best that is given to the system.
Some apps will directly support specific devices. Usually this is so they can access the extended metadata available from the device (NMEA). The extended metadata often includes the actual accuracy, higher resolution altitude readings, satellite positions, and other things like that. This metadata isn't required for the latitude and longitude and that is presently the only data Landscape Mobile uses.