That's a good question! My understanding is that no, your body doesn't get used to exercise in the sense that it takes more and more to achieve the same effects (it may get used to it in the sense of being in better shape and needing more intensity to continue to build muscle after a certain point).
Exercise does two things in relation to BG. One, it burns through glucose as fuel for the active muscles, which lowers BG directly, during and immediately after the exercise. My understanding is that this promotes fat-burning later on, as the glucose the body would normally use to fuel it's regular activities (beat the heart, digest food, expand the lungs, heat the body etc.) has already been used up. When runners "hit the wall" it's the point where they've exhauted their easily-accessible glucose stores and the body is looking for another source of fuel.
Two, it sensitizes the insulin receptors in the muscles that are used and built up. That means that it takes less insulin to "open up" the receptors for glucose to go in to the muscle cells (and out of the bloodstream i.e. a lower *blood* glucose). The purpose of this is to allow the muscles which are likely to be used in your next activity to have easier access to fuel - "if we needed a lot of fuel today, we might need it again soon!" This is what is referred to when someone says that exercise reduces insulin resistance. Consider that one of the causes of high BG in diabetes is that the body isn't able to produce enough insulin to cart off all that glucose, either because there's just a lot of glucose (e.g. from a high-carb diet) or because the insulin receptor cells are resistant and need a lot of insulin to open them up, or a combination of both. So reducing the amount of insulin needed to open up the receptors helps reduce the amount of insulin overall that the body is able to produce, which means the body is better able to keep up with insulin production, and keep BG levels in range.
I'm not sure I explained that clearly? But skip to the end, as long as you maintain a certain minimum level of activity, the receptors will stay sensitized. And it doesn't have to be "exercise for health" i.e. in a gym or a class. Anything that gets you out of a resting state (anything more active than sitting or lying down) will get you some improvement. So standing is better than sitting, walking better than standing, etc. Of course more strenuous exercise gives more obvious results, but you don't necessarily have to run or grunt or sweat to get benefits! Anything you like to do counts - playing sport or even just gardening or going for a stroll, every little helps.
Think of your goal as not to "exercise more" or even to be "active" or "sporty", but to lead a life that has more movement and activity in it than before.