They did, it's called gensurf. Least from what reading I've done on the subject.
"Our primary tool was a plugin for Q3Radiant , created by David Hyde, called GenSurf. The tool was originally created for Quake 2 (and may have been around longer) and has been adapted for use with many of the game engines using Quake, Quake2 and Quake3 technology. The basic concept behind GenSurf is that it can create and export a group of brushes (or curve patches) to Q3Radiant that have the look of “natural” terrain about them. Within the plug-in, the mapmaker has control over the horizontal dimensions of the terrain entity, the steepness of the slopes it creates, and the number of columns and rows of triangles that it subdivides into."
Thats from the terrain manual. I've yet to try doing it, but I know Aries has done it, and Shadowspawn has been experimenting.