Lossless codecs should not look any different if using the same colourspaces, unless of course the codec or capture system has a bug, or is using a LUT during capture and mapping the pixels differently.
I'd be interested in a side by side compariosn, noting what program and card you used for the captures.
Also, if you could convert a logarith video to huffyuv (once again keeping the colourspaces indentical) and see if the degradation still occurs.
I'd be very surprised if they are different unless one does some preprocessing that the other doesn't, but it would be good to know.
The reason we chose huffyuv is it is
a) lossless
b) Stable
c) Fast
d) Capable of RGB and YUV/YIQ colourspaces
It is important when capturing such massive files that you don't drop a single frame.