I do not have the 2013 Professional version of Visio; however, for what you are asking can be done in any version...So, here is my input:
(1) Group all of the shapes that you are wanting to be within your outside dotted line;
(2) Use any shape you want to completely cover the grouped shapes and send that shape to the "back" (or, behind) the grouped shapes;
(3) Remove the background color of your shape (or, recolor to what suits your needs);
(4) Change the outside line of shape to dotted, dashed, or desired line type;
(5) Group the entire objects/shapes together as one.

It has been awhile since I last used Visio in a professional environment, so hope this works for you.