No mission givers and engineers are not persistent NPC because like us there is no way they can be in 12 stations all at the same time.
It is a misconception to believe they are persistent NPC's for all those that did not play Elite Frontiers or Elite First Encounters.
A persistent NPC would only be seen in one station at a time or may ask you to help them get to a safe location i.e you take them some were.
Or they may be flying a ship that you help and because you helped them they may give you a mission or become friendly with your Cmdr.
As now seams to be the normal way Frontier are not really adding the game content they keep saying they are working on.
To check just check out some of the recordings that Frontier used to show what they were supposed to be working on, ship mayday calls were you interact with the ships you rescue . Its sad but is now a fact that a very large section of people that bought Elite Dangerous are so disappointed with the game they no longer play.
And just to point out i am an extreme backer i have three accounts and know one day soon i hope Elite Dangerous will be the only game i ever want to play. But Frontier need to start adding the content they keep saying they are working on
All the engineers are persistent NPC, all the mission givers are persistent NPCs. If you are talking about persistent ships, then no.
Even same faction bases would not have the same NPC giving you missions each base would have a different station commander or faction leader in the station.