What can be ashamed of in his situation? He is a warrior, lost his hand and was disfigured during the war, like an ordinary soldier. And then not even Valky's fault, because he honestly warned that Arcann should not take part in this attack.
Hard to tell. I think, in addition to the usual feelings of a disabled soldier, there is still resentment towards the father and anger at himself for his ill-considered act. But if he was ashamed of the scars, he would simply never take off the mask.
By the way, why does such a developed civilization, like Zakuul, have such primitive prostheses? They could easily make a biological prosthesis indistinguishable from an ordinary hand.