From an Adobe help file when rendering to Cineform: "The GoPro CineForm codec can encode pixels in YUV 4:2:2 at 10 bits per channel, or RGBA 4:4:4:4 at 12 bits per channel. "
I just rendered a 4k clip to Cineform RGBA 4:4:4:4 from Vegas 13. MediaInfo does not report the bit depth of the rendered avi. However, the source above, along with anecdotal information scattered about the web, indicates that the Cineform file is 12 bit.
EDIT: I assume you know that installing the free GoPro Studio, even if you don't use it, gives you access to all Cineform codecs in Vegas and other applications.