NO, to use copper paste with any metal other than copper may be a problem later on. Vasoline may be ok too, but it may have some additives that could affect some types of metal. I prefer one of the many products that are made for this application. We typically refer to them as NO-OX.
If you don't have NO-OX, then use the Vasoline, as it is better than allowing in air that contains humidity.
Yes, I work in telecom now and on the wireless side. The copper wired side (standard house phone technology) uses even larger copper cables in the switches and those folks really do know the business. On the wireless side we use cables in cell sites that usually don't exceed 4-0.
The whole idea is to keep ambient air out of the crimp. Crimping is a whole technology by itself and very few do it correctly. When I find installers at a cell site doing power work, I always casually watch them crimp. Few have a clue and weren't trained correctly, or at all. That is why we have a 200-300% safety factor designed in. Still, I sometimes go over, by hand, the connections and find some of them to be hot to the touch. Many of the contract workers have learned to fear/hate me. It only takes a few more seconds to do the job correctly, so why not do what you are paid for?
Ask the Indians what happens when you don't control immigration.