There are laws on how far things can extend beyond certain parts of a vehicle such as the bumper but nothing in regards to actual bars and such. If that were the case then most plumbers trucks would be illegal since they have those racks running down the sides. All running boards would be illegal, nerf bars, etc, etc. There are laws the limit actual width of a vehicle or other mirror requirements but a roll bar being illegal haven't heard of that. Some Land Rovers have external roll bars like the D-90 so they would be illegal too.