Chumming works for all fish. I've never specifically chummed for crappie, but I regularly catch crappie when I chum for other species.
Bob McNally has written articles about it in Crappie World. They would sink some type of grain to draw in minnows which would attract crappie.
There was also an article in In-Fisherman about a Florida saltwater guide who chummed for bass. He would throw out a cast net and load the boat with small shad. Then he'd chum with the live shad. He called it "power chumming" and was very successful. I'd think the same technique would work on crappie, white bass, hybrids, etc.