Yes, you can marshall to create ...
If you create a pptx containing SmartArt in powerpoint, then run the result through the PartsList sample, you'll see which part classes pptx4j uses for the SmartArt parts.
For example, one is
Using java Syntax Highlighting
public final class
Parsed in 0.013 seconds, using GeSHi
CTDiagramDefinition is in package package org.docx4j.dml.diagram, as are the other SmartArt related content objects.
The Diagram*Parts are in org.docx4j.openpackaging.parts.DrawingML
All of this stuff is in docx4j's src/main/java dir tree.
hope this helps .. Jason