Probably not necessary, but I always do it on small blocks since I don't want to have to pull a freshly sealed oil pan even if it's still on the engine stand much less in the car. Most of time simply spinning the pump with a hex shaft will suck oil without any vasoline or other help, but I don't want to chance it. Big blocks with their external pumps I am not that concerned about. On big blocks I just make sure they have some oil in them. I've never seen where the vasoline does any harm.As far as avoiding the need to pull the distributor and drive gear is concerned, so long as the engine already has oil in all the galleries,bearings, etc. then no you don't have to do it. If it's a fresh unfired engine then yes do it.