Very rarely does a bird not have some damage when shot. I'd rather fix a wing than try to fill a pellet hole/s in the head. Fixable? By all means, yes. Sometimes the bird looks absolutely flawless from the out side, and people cradle them like their holding a newborn baby. Then it makes it to the taxidermist, and he skins the thing, turns it inside out, fleshes it with a wire wheel, washes it, tumbles/dries it. runs wires, and then gets back to the preening. In other words the bird goes through some abuse in the taxiing alone. Not to mention one that looks fine on the out side, and was shot three times because it was a cripple, or a hard-mouthed dog put his chompers on it, or it is full of pin feathers, etc. etc.
Bring it to your taxidermist, and he'll tell you if it's a go or not, but it should be fine. I would think that a Shoveler shot this late in the season would be in great plumage, and they sure are a pretty bird when they are full-feathered.