It depends on what you mean by "work" when you ask if it works to complain. If you mean receiving some form of compensation, then yes, it usually does work ... if you instead mean that the airline makes the changes to avoid a similar situation in the future, then no, complaining rarely works.

The IAD UA baggage staff are largely awful IME. There are a couple of good ones there, yes, but largely they have come across to me as lazy and incompetent in my dealings with them. Fortunately, with the lines what they are at check-in these days, I tend not to check bags and don't have to deal with them, although sometimes it's unavoidable.

A short tidbit from one of my experiences with IAD's baggage staff: when I lost my cell phone while boarding a flight, I filled out a claim at IAD and was given a number to call (which was answered by a full voice mail box). I called the UA staff at CRW, and yes, they had found it and were putting it in a box and sending it on the next flight. IAD's staff then LOSES that box, as I discover after a wasted trip to the airport by my wife. I spoke to the apparently one helpful person there who says he's going to look for it, and he leaves me a voice mail late that night saying he found the box and has left it with the baggage desk. The next day when I go to pick it up, the baggage office staff claims they have no idea what I'm talking about and are mad at the helpful guy for "committing them to something without talking to them." All this time, my box is sitting right behind the woman I'm talking to.