I think it depends on the individual show in regards to whether opening night tickets will be released to the public or not. I've attended the opening night performances of The Heiress, The Realistic Joneses, The Audience, and Finding Neverland, for which all of those shows had released tickets to the public.
"Mostly, I loved the size of these people's emotions. Nobody has emotions this size anymore. Outsized emotions. Operatic emotions. Kushemski and Vanda are like Tristan and Isolde, they're Paolo and Francesca. Nobody's in total thrall like this anymore. Nobody's overcome by passion like this, or goes through this kind of rage." Thomas, Venus in Fur