Yeah, as has been said, he didn't really whine. He only really complained on a few occasions, and beyond that he mostly just remained quiet. He was kind of grouchy, which I suppose some people could take for whining, but it's not really the same. He was very bitter, not whiny, but bitter. We aren't given any official insight into his past, so that could be with or without reason. Without a reason, it leans more towards whiny territory, but he still never struck me as whiny.
I personally believe that he had some form of mental disorder, as some of those can make someone feel victimized and bitter even when they are loved and well-off. Something like that would explain his personality as well as his physical condition, because many people with mental issues have trouble taking proper care of themselves, and in some cases, don't feel hungry enough to keep on weight, and things along those lines. I'm not saying he was schizophrenic or something because he obviously wasn't acting like that, and he was consciously making his decisions and plans and going along with them, but there are some disorders like depression or bipolar, or some of these mood disorders that, in conjunction with a desire for power, could quite easily create the villain we see in the movie. Of course, a strong enough lust for power could result in something similar, but based on Scar's bitterness, I don't think that alone is the cause, plus, it's less interesting if he's
just power hungry.
At any rate, I wouldn't call him "whiny."