Went to take a look at the creationkit wiki again
Unique Actor - Pick a Unique actor to fill the alias. Note that this will only work if the specified actor's reference has been assigned a Persist Location. (see http://www.creationkit.com/Object_Reference)
So I created a new location and added the cell the priest is in + a nearby cell. On the map this works, and when I look at the small map it also shows the name I assigned it, so the location works.
I tried putting the SetObjectiveComplete(10) on the alias of the priest, but no change either.
no quest markers show up and the npc still doesn't spawn.