Yes the keyer returns to the "raw untouched file" when using pro-res. This is what you would expect.
However with RED files it goes a step beyond raw untouched file to some kind of pre-metadata image. If you are shooting something close to the sensors native ISO, color balance etc you might get lucky and have a usable image. Shooting on tungsten at a high iso, you get unkeyable mush.
You can simulate what the keyer sees by disabling the RED page in primary grade. The resulting image is equivalent to what the keyer sees.
While you can grade by adjusting RED metadata, a files original RED metadata is more correctly though of as part of the "raw untouched shot" than part of the grade. ISO, Kelvin, Tint, Exposure, gamma and color space - while they can be edited in post, are decisions that are made at the time of shooting and integral to the shot.
Here are some examples - Original shots with no adjustments whatsoever, metadata or otherwise, and the same shots with the RED page disabled, which illustrates the difference between what you would think of as your raw shot, and what the keyer sees.
