Certainly when my iPad 2 is tethered to my iPhone 4 via Bluetooth the iPad has accurate GPS data. We use it often while traveling in the car for live mapping, and my iPad 2 is the WiFi only 3G model (but without an active SIM card) which does not have it's own GPS receiver.

I have not tested whether the GPS data is also available to the iPad when tethered to the iPhone via WiFi Personal Hotspot, without Bluetooth.

Edit: I have two iPads, one with 3G and one WiFi only. I may be in error as I have used both in the car, but apparently I have not have properly verified map updates with both.

About to update iPad to iOS 5 and new iPhone 4S. Will report back later.