TickleMeMya, you asked such an interesting question that I decided to search the web for a possible answer, and while this isn't definitive, I think it's one example that a stump can indeed be ticklish. And no, I'm not an amputee fetishist, but I wouldn't mind tickling one either (the amputee, not the fetishist).
Link:
TuckerMax.com
Excerpt:
I don't have an amputee fetish or anything like that. I kinda mentioned this in passing, and a girl I know worked with a girl who lost her lower leg in a car accident. This girl was pretty hot, we hit it off and ended up hooking up...but I had to get pics because I could not pass up the chance to cross another thing off my Sexual To-Do List.
EDIT: I forgot to mention the best part: She was totally ticklish on her stump. I would rub it and she would giggle and squirm. It was awesome. She could also wiggle her stump muscles. It was spooky.
I hope this helps you do you "homework," Mya.