To me, there is nothing indecorous about "one-legged," but it sounds more natural preceding a noun than after "he is..." In other words, I would say "A one-legged man came into the room." but "He has only one leg" rather than "he is one-legged."
Sorry, I don't remember the grammar terms for the two different positions of adjectives. My guess is that the adjective after "he is" would be a predicate, but I'm really not sure.
This thread reminds me of a sports event I saw years ago on TV, in which several one-legged men were competing against each other in a high-jump event. It sounds like a bad joke, but it was really an incredible thing to watch. After a series of preliminary hops, they would just spring up into the air and over the bar as if on a pogo stick. Amazing.