Certainly, regarding Bill Willingham's "traditional superhero."
There are two basic beliefs behind the superhero concept (powers or non-powered):
1. There are problems too great for established agencies to solve.
2. If you are able to help, you are morally obligated to do so.
In the case of #1, from Superman to Indiana Jones, superheroes are people who become aware of a problem that they are convinced the regular law enforcement, judiciary, and other societal resources cannot fix. The problem is too big one way or another. Not that such observations are necessarily liberal. This is a prerequisit for the motivation of any kind of hero. But heroes in general take it upon themselves to solve a problem rather than wait around for others to do it. (This is not to be confused with conservative do-for-yourself principles, which means you help yourself and let the other guy help himself...and if the other guy can't, well too bad.)
In the case of #2, this is true for the "traditional superhero." And it is the very basis of liberal activism. If you have the means to help, it is a moral imperative to do so. The New Deal, Great Society, Affirmative Action and so on. (Speaking to their motivations, not necessarily their successes.) If we can spend tax money on law enforcement to improve society, then we can also spend tax money on other things like health care.
Superman and Indiana Jones do not act for personal gain, but to right a wrong. Typically, the trad s-hero is rewarded only in praise and a doctor bill. His power is not used to feather his nest. This is the opposite of conservative (i.e. capitalistic) uses of ability. It also illustrates a whole-world philosophy. Superman seeks to help everybody, because he sees the world as one communtiy. If we let strangers suffer, we all suffer; the world is a worse place. Conservatives generally more tribal, that their tribe exists independent of other tribes. Do for your own tribe. If you altruistically do for a different tribe, you're just hurting your own tribe. And let me throw in that superheroes are by definition activists, and we all see how conservatives react to meddling activists--they demonize them.
It is very wrong to say that liberals have gotten ahold of superheroes and turned them into liberals. That's simply because superheroes have ALWAYS been liberal. It's the basis of superhero DNA.