How to compensate for red oversaturation and contrast increase?
Unfortunately, even if you could get an exact amount of the difference, it is highly unlikely that adjusting by that amount will fix your problem.  Since a lossy compression is being used, the codec is deciding to alter the color to something that is more easily stored in a small space.  You will likely get a different color artifact if you try to correct for this one.  Your best bet would probably be to look in to the formats that Vimeo uses and try to encode it yourself such that Vimeo won't have to transcode it.  This would give you control over the compression itself and you might be able to use a better encoder that would maintain color more accurately.