Does this work with a stacked bar chart using the group= option? When I try it I get this note and the vline is not visible on the graph:
NOTE: Grouped line charts are not stacked. Overlaying them on a stacked bar chart might make the chart difficult to
interpret.

proc sgplot data = fullstack ;
vbar admitYr / response=total stat=sum group=name ;
vline admitYr / response=ncost markers y2axis group=name;
run;