Gingersnaps, mushed up, are what I use for pumpkin pie crust, like it much better than regular or graham cracker crust. I agree with Addie, they would probably be great as a topping too. Maybe mix with some melted butter and sprinkle over top. Not sure I'd mix the crumbs in.
Treat the cookie crumbs the same as you would the graham crackers. Mix with melted butter.