No, 3D Studio uses only triangles, even in release 4. However,
they do use the trick of having a flag for each edge of a triangle
that sets whether that edge is drawn in the user interface or not.
When you build say, a cube, with their built-in tools, it
sets the diagonal edges of the faces invisible, which gives you
the impression it allows >3-sided polygons. You can also
set the visibility of edges yourself if you prefer confusion.
When my company's InterChange file format translator creates
a 3D Studio file from a model in another format that supports
polygons, we set the edge visibility flags so that you see the
same "polygon" edges as the original object.