I might be out of my depth and not truly understand what is meant by abstractions, but I think the answer is yes?
Lets look at the example on the website, theres a node called cube. Isnt that little node an abstraction of a whole lot of other things? A more advanced visual programming language would allow you to access and modify what a "cube" is. You would be able to double click on that and be taken to another graph. This graph would be about the construction of a cube and would take input of width and create triangles in space to represent a cube. you could double click on the triangle node and be taken deeper, this time a node that takes vectors and defines where the surface is between them and sends it to the renderer. We could have a seperate graph to define what a vector is and the data structures behind it.
All of this for a simple cube could be represented as a huge tangle of nodes and connections, but we can condense it down to a single node called cube that takes an input of width.
Having networks and sub-networks allows you to choose what level of abstraction you work at. Each of these things at different levels can be represented by a graph.
