No you do NOT need a Sim installed at all.  The GPS receiver on your device will show you where you are on the map. The App Geolocates all the time.

The devices’ GPS must be on and the app must be allowed to use the location service of the device. None of these are dependant on a SIM card being present.

The APP will continue working without Internet signal, but needs location functionality.

Its just that on Apple devices, only the devices with 3G capability has an installed GPS receiver, and you will require that in order for our apps to work on your device.

iPADS:

If the I-Pad does not have have 3G, it does not have a GPS Receiver,  iPads with only WiFi does not have a GPS receiver built in (but can still determine your approximate location when in range of a WiFi network).

You will still be able to use your Ipad to view the Map, but you will not be able to see where you are on the Map, unless you are within range of a Wi-Fi network.

Also, due to the limitations coming from Apple, any iPad without 3G wont work with GPS positioning, no matter if its paired to another GPS capable device.