The developers of the other game have much lower requirements for what's necessary to get a vehicle in game. Hence why they have some vehicles that were nothing more than a single sketch.
We do also use private and paid sources. Nobody said we did not.
But so far there is nothing to suggest that any private documentation on the O-I contains any of the material needed or is worthwhile of the probable costs of a deal, if such a deal would even be possible given as you said, another game has already done so. The 3D model is not all thats required for the O-I to be realise