I would see two issues with conductive greases... The ones I am familiar with are very messy when they migrate (hands, cloths) and can get into electronic circuits and cause shorts/failures.
The above issues with silicon grease are much less/non-existent. However, there is one issue to be aware of with silicon greases... It can be very hard on small switches. Even the fumes from silicon grease can get into fine switch contacts and cause them to fail open. For example, silicon grease, in the "olden days" could eventually (and has) disable an entire telephone switch room just from some silicon grease on a entry door (we had to certify our equipment did not use silicon grease for phone companies).
To be honest, I have not heard of anyone having contact failures with silicon grease and flashlight contacts--but if your switches seem to be getting dirty/failing often--you might try washing out the silicon grease and using something else.
That is why it is usually better to use a contact lubricant, like Gold Mist, or other types of lubricant designed for electrical use. Although, I use automotive silicon grease on my flashlight "O" rings and threads too.
-Bill
