Define "does not seem to work". With "block", which was a new tag type added in 13.0, you said you got the wrong bitmap. What bitmap do you see when you use "statement" instead of "block"?
The callback is checked in _are_statements_supported(), which is in listproc.e. True, it really doesn't make a tremoundous amount of difference, except for enabling the menu option to show or hide statements in the Defs tool window. In your case, since you are inserting statements using sort of a back-door mechanism, turning off showing statements in the Defs tool window won't really make a difference anyway.