They both have the same ingredients, however there are some differences. The difference is in how they are made and how they are used. The collagen hydrolysate is easier to use. I bought the gelatin but I so wish I had bought the other form. It clumps if not in the right temp water, basically warm.
The below gives an excellent overview of both.
www.hollywoodhomestead.com/difference-gelatin-collagen/