Help please clarify.
I intend on using the ipad2(wifi version) tethered to my droid x as a gps in my truck. Will it work properly or do i need a 3g model?
No, or at least not very well. There is nothing in the WiFi tethering that will pass the Droid X's GPS data to the the iPad.
The iPad will probably still try to locate you using the WiFi location features. How well that will work depends entirely on where you are; how many hotspots and if they are in Apple's database. Even if it finds you, turn by turn instructions are going to be terrible, if the iPad even tries to deliver them. Wifi location is rarely more accurate than a couple hundred feet. That is for the build in Map application.
Third party navigation apps built to work with the GPS are even less likely to work properly.
If you need accurate GPS data on you iPad the best, easiest, way to get it is to buy the 3G version. If you already have a WiFi only iPad and need GPS, then you might want to fool with some of the alternates. Because then you are looking at the price of a new iPad to cure the problem, instead of the comparatively cheap $130.
Note again: You do not need to buy a data plan for the 3G iPad in order to use the GPS.