Does a brace help a pars defect to heal?

No. To my knowledge, pars defects do not heal. Some authorities think they may be congenital or developmental. However, you can have normal function despite the defect, by building up your core strength to compensate for it. Abdominal and side strengthening, supervised back strengthening exercises, even yoga are all beneficial. I would recommend seeing a good pt for help with such a program.