If you buy the iPad new, they may require a data plan depending on the deal you get at the store.
If you buy the iPad used, no dataplan ia required.
Regardless of those two factors, you do not need a data plan for the satellite chip to work. Data plan would be for cellular, satellite chip is separate. They just only put the satellite chip in the cellular model.
The beat way to test the chip is to put the iPad in Airplane mode, then open the Maps app, drive around, and see if it tracks you. *Airplane mode turns off the cellular chip, but not the GPS chip.
(I know they aren’t really chips, I’m just keeping it simple)
James