It would definatly help ground forces rid the area of wraiths, lucusts, and scarabs but the covenant could still just glass the planet.noIt's possible. However, A-10s have next to no anti-aircraft capability, so they would be outmatched against Banshees. Ever seen Terminator Salvation where the Terminator fighter takes down the two A-10s? That's probably how it would play if the UNSC used A-10s. But A-10s would probably be very useful in their role, taking out Wraiths, Locusts and Scarabs if they operated in large numbers. If the UNSC also used F22 Raptors... it's be a game changer.
If both aircraft had shields. (DeltaBomber58, original inquirer of this question)