I have never tried using a subUV on ribbons, but by nature of how the UVs are generated I would be surprised if subUVs are supported.
SubUV on a ribbon would probably look very strange, the idea when texturing ribbons is to use the two separate UVsets to tile patterns at set distances in one UVset, and mask along 0,1 in the other UVset.
Try mousing over the Tile section of the Ribbon module and read the tool-tip.
Using some techniques with panners, UVdistortion, multiple textures moving at different speeds can yield you some really cool results on riboons, animTrails, and Beams.