Is it safe for people with scoliosis to ride roller coasters?

Yes. Most patients with adolescent idiopathic scoliosis should be able to ride roller coasters without a problem. Ensure that the seat belt and safety mechanisms fit comfortably. Patients with severe adult scoliosis may have "soft" bones due to osteoporosis. These patients are at higher risk of getting a compression fracture of the spine and thus should avoid roller coasters.
Yes . Usually there is no issue once you are fully fused and have been released to sports but one should avoid contact sports. If never had surgery, no problem!