Does getting any job (no matter how demeaning) builds up one's character? A certain blogger claims that 


  [if you] Work a shitty job, it builds character [nonetheless].


I'm curious if there are any academic studies relating to this issue. Of course one needs to consider the definition of job carefully in this case: does prostitution count for instance (it's legal in some countries), or does drug dealing, i.e. are we talking about income, legal income or just doing work; what if it's unpaid work, e.g. volunteering? It would be really nice if some study went to such extents to distinguish between these in relation to the outcome..., but I'll settle for more generic descriptions of "job".

Also one would have consider what exactly "build character" translates into (psychologically speaking)... enhancing self-esteem, or something else I haven't thought of just yet. But I'll leave this aspect fairly open as well.
I suppose much depends on what one means by "building character"; if it's increasing self-esteem, then the answer is probably no, as you've already pointed out.  But I don't think that's what most people mean by building character.  So what is it?  Certainly you'll learn something from having a demeaning job, because you'll learn something from just about anything; also, it is likely to lower your expectations, so you might be more excited about any given other job and value the money you earn more (see for example this article).  So it's probably possible to adjust the definition of "building character" until it's mostly true.  But after twisting the definition too far, it's unclear that "building character" is a desirable thing to do, so it doesn't offer much in the way of advice for life.

Incidentally, it has been argued that most work in the US is actually fulfilling.