Digital Light & Color

...add the capability to create text on a radius, e.g., to form a semi-circular arc of text...

With a bit of experimentation, you might get the "Geometry/Fan" transform to do what you want...See also:
(1) http://www.dl-c.com/discus/messages/523 ... 1181966805 and
(2) http://www.dl-c.com/discus/messages/2/5281.html

As a workaround, you can use the Transformation/Special Effects/Fan transformation to warp text in a semicircle.