Have you followed the steps as outlined in this Wiki on how to create a DataGroup Annotation Cell to be used in a drawing rule?
communities.bentley.com/.../7624.associate-a-new-datagroup-type-with-a-datagroup-annotation-cell-for-a-drawing-rule
communities.bentley.com/.../7624.associate-a-new-datagroup-type-with-a-datagroup-annotation-cell-for-a-drawing-rule