Skystrike missiles get a +1 to hit air targets; if you move and you're shooting an aircraft with -1 to hit the Skystrikes will be hitting on 5+ where other weapons will be hitting on 6+. The Vulture isn't a good plane to carry an AA loadout. (You can tell it's built for air-to-ground by Strafing Run (+1 to hit targets without Fly))
The other problem with Skystrikes is that they're horrendously overpriced; from a purely practical standpoint a 108pt Hydra is a better AA unit than a 240pt skystrike-autocannon Vulture, as it's got almost as many shots (8 down from 10), they're way more accurate (hitting planes on 4+ instead of 5+ and 6+), and you have access to a lot more support abilities to make them work better.
If you like Skystrikes and want to find somewhere to put them a Lightning with Skystrikes is all of 5pts more than that Vulture and as it starts at BS3+ the missiles are a lot more accurate against air targets (plus you get the lascannons hitting air targets on a 5+). If you just want some Navy air support a Thunderbolt or an Avenger is cheaper, at least as good at AA due to the starting BS3+, and more flexible since it doesn't have to weaken its ground attack loadout to shoot aircraft.