Just an oppinon, but die electirc grease, is mostly to limit corrosion/keep moisture out and make some sort of moisture seal. It almost has to be resistive, so it doesn't cause shorts. But when it has a thin enough coating, passes enough juice, that the resistance is hardly noticeable.
Your silicon grease may or may not pass enough juice. I'm sure the design properties of die electic grease, took the resistance factor into consideration.
I don't realy know about your silicon grease. What does the label say?