What are these wooden glass dividers called (cabiner window dividers)?
That part of the window is known as the &quot;muntin&quot;, so these would be &quot;curved muntins&quot; - although I couldn't find much about them.  From the pictures you posted, it appears to be some kind of thin plywood, with the outer layers oriented perpendicular to the window surface to better bend.  Veneer is definitely also an option, and probably the simplest way to get wood that thin.  Most of the structure holding the glass just comes from the glazing.
If you do use veneer, try to orient the pieces so that the grain helps you bend them, don't try to bend against the grain.  Some steam, or ironing them between damp cloths might help.