@swinxx - I fully understand what you are saying but I think you have the wrong idea about raw images and colorspaces.
Cinelog-C does not transform the DNG itself. It transforms from the colorspace to which the DNG has been debayered. In Resolve we transform from BMD Film and BMD Film 4k.
The DNG has no colorspace of it's own but has color matrices that tell the raw reader (in this case DaVinci Resolve) how to map the camera's RGB pixel values to CIE XYZ colorspace. It is the BMD workspace that is the colorspace.
Put in simple terms - Resolve reads a DNG and performs a transform from Camera RGB values to CIE XYZ. It then transforms again to from CIE XYZ to BMD Film colorspace which is a very wide gamut colorspace with a logarithmic transfer function and defined white point - all in a 32bit floating point processing space.
This means it does not matter which camera generated the DNG file so long as the color matrices accurately map to CIE XYZ and this is the reason why I submitted the Adobe color matrices for all MLRV capable cameras to MLV developers a few weeks ago. These matrices have been developed under lab conditions - as have the ones in BM camera DNGs.
Differences in camera color are caused by RGB channel cross talk and noise. A very good sensor such as the Alexa's Alev III dual gain CMOS sensor has very good control over crosstalk and very high dynamic range - this produces a cleaner signal and more accurate color. The 5D mark III sensor is very good but has more crosstalk and noise meaning it does not produce color as accurately as the Alexa - not surprising considering the price difference! A low-end camera sensor usually has appalling crosstalk.
Anyway, what you want to know is if the 5D mark III can produce the same color as the BMD Cinema Camera - The short answer is that it already does in a raw workflow.
Cinelog-C does not support Resolve REC709 colorspace the luts only work from BMD Film and BMD Film 4K.
REC709 is a delivery/display colorspace (you can work in it of course if you are going from raw to deliverable without a digital intermediate like Cinelog-C). REC709 has around 6 F-stops of dynamic range with relatively small RGB chromaticity. This is no good for encoding a digital intermediate and is one of the reasons why log and wide gamut colorspaces exist.
I've had several people ask why can't you use REC709 with linear gamma - well, there is a big difference between scene linear (integer values mapping the whole signal within the containers bit depth) and Linear gamma. Linear gamma REC709 is still REC709 colorspace but has a gamma of 1.0 - It is a tiny colorspace compared to BMD Film and Cinelog-C.
Hope that explains it. I'm not sure I can explain it any easier
