Is silicone caulk an appropriate sealant for keeping smoke out?
Any caulk will seal an area. I would refrain from using silicone, since it does not take paint.

A decent grade painters caulk will do you very well and can be painted too when the color scheme needs to change. If you want, it is also available in clear. Typically it goes on white, then dries clear, and is water cleanup, another advantage of painters caulk over silicone.

Silicone does have its place, here is not one of them.