We don’t know. Perhaps he is immune because he was the focus of that wish, but it’s not likely. His Ether is really the only thing that got affected and it’s supposedly not even an unlimited source (Fikrul and the Barons were artificially producing new Ether, meaning Fikrul wasn’t producing any himself), so it seems Fikrul is the same as all other Scorn. He probably is affected by the negative effects. But because of the limits caused by it being a game, we can’t see any change and won’t know of any until Bungie reveals it.