I tried to learn about this subject awhile back but there was not a ton of info. available online. The one thing I did learn is that it's the different bases that greases are made that can make them incompatible.

I have also read in the Barnett's manual not to use automotive grease in bike bearings. Unfortunately he did not say why. The only thing I can figure out is that auto bearing grease is too thick and will cause excess drag.

I'd like to hear more about this subject from someone who is a grease expert.