Depends on how you make them. Some people poach their balls in the sauce. Frying them on a pan will brown them, but plenty of fat still inside (as you don’t completely cook them through, but add them to the sauce to finish.) If you bake them in the oven then, yeah, a good bit will render out.
At the end of the day, if you’re that worried about grease, just buy leaner meat to begin with. I’ll stick to the 80-20 chuck or fattier, myself. I do tend to pour off excess fat, though when I’m frying up ground beef for a casserole or whatnot. I’ll leave enough in there to fry up the onions and whatever other veggies I may have going in.