Be sure to "draw" the features by using the current map units (need to project the points to the current spatial reference defined in the map). One place where this can be done is in the function which implements the override to the abstract method "DrawDynamicLayer". Other place where this can be done is when reading the points from the dynamic feed (be aware that in this case it seems that you would need to re-read the points each time the spatial reference of the map is changed).