Saltwater guys chum like this all the time. Chumming absolutely works. I've never done it specifically for crappie, but I've caught crappie while chumming for bluegills. I've heard of one guy in particular who chummed with small shad for bass and was very successful.
Chumming is an art, not a science, though. Most people chum WAY too much and mess it up.
I mostly chum for bluegill and carp, and it's deadly. The difference between chumming and not chumming is like night and day. You really have to see it to believe it.