Hi,
Of course this is also a valid thing to do, though as you notice, when the graph segments are drawn with the red dotted line, it's shapes can not be created properly. This may sometimes give you a few issues.
Though in the end, using the 'Dynamic City Layouts' system is just the process of creating shapes, for later use in CGA. If the shapes you create give a valid topology for your work in CGA, your goal is reached.
So yes, go ahead and also use that trick ! sure !
Matt