I do try to hide my pump, and I did when I was applying to jobs and when I worked.
Part of the problem is that the hiring people can't directly ask about certain things, but they do look for clues to weed people out, sometimes illegally. I've been told this by a few different people, some at my college's career center, and other people who confirmed it elsewhere.
For example, they can't ask if you are married or in a relationship, so the look to see if you are wearing what could be counted as a wedding band or if you have signs of having worn a ring on that finger for an extended period of time.
I was told that they do look for signs of disability and will look for insulin pumps by looking at pockets (if the object in the pocket is not cellphone shaped) and by looking for tubing.
They may also try to make you bring it up by having a meal or snack during the interview process, which for us means checking and taking insulin, or refusing food and unloading that baggage.
If you bring it up, it is considered fair game and they can ask questions.
While it's illegal for them to not hire you because of diabetes, that doesn't mean they don't do it, or that they won't try and pass it off for a different reason.
And yes, while I agree that I would rather not deal with people who aren't going to accept me, sometimes that is not an option, especially when it comes to work environments.