If you've ever seen a car that has been burned completely, you've seen the seat frames inside. Seats these days seem to be nothing more exotic than a lawnchair as far as the frame goes. I'm sure they are high strength steel but they wouldn't save you in a rollover, likely just to not come apart or break like mild steel. Backseats are nothing more than a cushion that is "clipped" to the floor and a backsupport that clips and bolts in along with the seatbelt bases.
However, prudence being the better part of judgement, it would be foolish to recommend anything other than OEM equipment to place public or private passengers in. The world is too sue happy and unpredictable these days. You might get away with some individual camaro/firebird backseats if they have decent mounting points but that's a big maybe.