Unless my memory is playing tricks on me the original models were AWOL at the time Fallout: Tactics was made, which was why the FOT devs had to start from scratch without any proper reference material for the models (other than the renders, I guess).
It was also the reason the VB models were created from scratch.
Sure, the old models would have been too low in detail anyway, but it's better than nothing -- and you can always improve an existing model.
The VB models should still be around, tho -- that is, either somewhere at Interplay (do they even have an office again?) or Beth.