Any question answered...

Greasing the taper isn't for corrosion protection, its to get the crank boss far enough up the taper with the available bolt preload to cause the flank pressure under no torque load to be sufficient to prevent its dropping to zero on the unloaded side under service torque load. That's a physics problem.
That common lubricants might also mitigate the chemistry problem of dissimilar metals being left in contact in the open environment for years is a side benefit.