I don't think he'd do anything illegal by just ripping the models, unless he distributes it to other people. After all, he bought a product, and can use it for whatever personal purpose he desires.
Nope, it's not possible to rip them from Unity. It's mod-unfriendly
Actually, there's a way to extract them. You can even extract complete levels. As an example, here's a picture of the first area of Rupture Farms (in Cinema 4D):