Do I absolutely need to add sugar to this recipe? I am trying to avoid refined/added sugar this month . Thanks!

You could opt to not add in the sugar called for with the corn kernals, but I would still add in the 1 1/2 teaspoons to the flour/cornmeal mixture. Corn begins converting the sugars to starches once it is picked, which causes it to lose a certain sweet corny flavor. However, I find most modern hybrids are overly sweet to start with, and frozen corn no longer needs any help to cover things. However, baked goods can benefit from a small amount of sugar to help with browning. That amount isn't enough to significantly add calories, and won't make your muffins overly sweet. You could further reduce the sugar level by using less maple syrup, or even opting not to use any at all. Ham ought to be tasty enough without it.