Stage doors at closing performances are chaotic. Actors leaving with boxes and stuff plus family members waiting and helping them. Lots of activity. Actors are pleasant but with things going on unlike regular performances where they're just simply leaving the theatre for the night.
Most? Who knows? Some? Probably. I've been to a couple of closing nights and people did stage door but as with any stage door experience, I wouldn't count on people coming out. Also, closing nights tend to be particularly crowded at the stage door from my experience. It was difficult enough to just get out of the theater when I saw Falsettos. The Walter Kerr does not have a great sidewalk situation for stage dooring. Good luck though!