Though I did preorder the game I don't know if we will have Site B or any kind of Dino free roam since it seems like they didn't bother to give us something simple like a day and night cycle for each island. Hopefully this is fixed before release, at least make it optional.
The only thing that makes me think there might a Site B mode is the fact that the game is pretty similar to JPOG in many ways, similar enough that some devs obviously played the game or watched a lot of videos about it. The way the dig site system works, the way the fossils and amber samples are lined up and you have to extract the DNA from them, you can sell other things your team digs up just like in JPOG. The picture mode that gives you money for pictures and points that increase your park rating/reputation, very similar to what was in JPOG. I don't find this all to be a mere coincidence.