Banisher Priest and Timing
Yes.
As Banisher Priest's effect ends, the exiled creature is returned to the battlefield immediately, without using the stack. Since state-based actions are performed completely before triggered abilities are put onto the stack, by the time you put Festering Goblin's ability on the stack, the creature that was exiled by Banisher Priest is already here to be selected as a target.
Daniel Kitachewsky
L3, Paris, France
Rules NetRep