The Galaxy Tab contains a Broadcom BCM4751 standalone GPS chip which has A-GPS (assisted GPS). This means the 3G coordinates assist the intregrated chip for a better location reading when there is a 3G signal. The problem might be is this chip is integrated into the 3G circuit stack. Thus, you may get some erroring if a SIM is not inserted.
The simple way to test would be to power the device up without any password lock and the SIM removed. Try the GPS. It should work. but that will be conclusive.
The GPS does in fact work without your data plan. I'm using Google Maps and it works great. I'm guessing that the app caches the map data, then retrieves it as needed. Some tips to remember though;
1. GPS must be enabled.
2. VZW location services must be enabled.
3. Battery must be fully charged or close to fully charged.
4. Airplane Mode must be disabled.
I cannot get a GPS lock without the above conditions met. Hope this helps...