Unless a doctor told you specifically to avoid certain movements or told you the curve has progressed, or unless you're currently having issues moving, I'd probably proceed as if there was no actual problem, training-wise. Maybe include some regular mobility work and posture practice. Belt squats are a fine option, but full barbell deadlifts with perfect technique may be one of the best possible exercises for you. Start light, of course, but do work on them.
I'd probably agree with that, depending on the individual. But for reference, unless we don't have the whole story, the dude hardly has scoliosis. From the National Scoliosis Foundation: "...if a curve is less than 10 degrees, we don't even dignify it by calling it scoliosis. Instead, we might refer to it as a postural variation."
