I remember when you could buy packets of Knox "drinking gelatin". It was supposed to give you stronger nails and hair. My mom used it. I still remember the picture of a nicely-manicured hand holding the glass of prepared gelatin, on the box.

I believe it helps in that way, as does eating adequate protein, but I don't think it increases growth rate. It might lead to longer hair in that stronger hair won't break off as easily.