So if I read the cards right, you can use Stay on Target to attach Niles Ferrier to a DS vehicle, but not to a LS vehicle.
Stay on Target states that you put the Pilot into play on a target friendly unit, and Niles Ferrier can only be attached to an enemy vehicle unit if you play it. (which is good, because otherwise Niles would be way too overpowered, stealing the Falcon without even paying his 3 cost)
But what if you use Stay on Target in multi-play and you attach Niles to another DS player's vehicle? Do you then take control of that vehicle? I would say "yes" based on the second line of his Pilot power: " Take control of enhanced unit while piloted by this card." which doesn't seem to be conditional on him enhancing an enemy Fighter or Transport .