Hypothetical aircraft drag reduction
Consider that, without any hydrogen, the surface of the wing is coated in aluminum, a material with a sound velocity of 6,300 m/s. It's not the speed of sound on the surface of the wing that matters. It's the speed of sound in the medium it's passing through.

You are proposing a wing coated in hydrogen, but even if that could be made, it would still have to move the surrounding air out of the way. It is the "moving the air out of the way" that creates the mach effects.