Silicone grease is one that contains silicone and is used for a water resistant coating, basically a lubricant. Dielectric grease is one that does not conduct electricity, and generally protects from water. No, they are not the same.
Dow Corning #4 Compound ( DC 4 ) is a dielectric grease that also contains silicone. Pretty slippy stuff. Used to use the stuff to pull replacement ignition wires thru aircraft engine harnesses.
If I understand the difference between silicone grease and dielectric grease, silver grease is typically used for lubricating things that petroleum based greases might attack. I use silicone grease on the side panel snap pins to ensure they will not some day break off. The word Dielectric means High resistance to electric voltage potential. So for example, the material used outside of a spark plug would have a high dielectric constant, so that the high voltage spark can't jump through this material.
Dielectric greases are often used on switch contacts, which one would find confusing, since it is supposed to be an insulator. However, the grease is thin enough to provide a protection from oxidation on the switch contacts and still move out of the way when the switch plates come into contact.
Today, silver grease is used on switches because it both protects from oxidation and conducts between the switch plates.