I don't use dielectric grease. Maybe it would be a good idea in a high-humidity environment though if corrosion is a common problem?
Most cameras come with a plastic cap and rubber gaskets which can only be used if you are attaching the RJ45 end yourself. I don't trust these 100%, especially if someone else put it together, so I will typically wrap a tight layer of electrical tape around the seams. Coax Seal is of course a lot better than electrical tape for keeping moisture out, but I normally only use it if I'm connecting a camera without a manufacturer-supplied rubber gasket and cap. And if the connection is in a weatherproof box with no way for water to run down the cable and get inside, then I wouldn't bother with any of that.
Boots on the male RJ45 connectors don't really matter either, since these won't be something people are regularly unplugging or pulling on. If you have them, then sure, why not, use them, as long as they fit inside the cap.