Does boiling meatball remove some flavor
You can certainly poach meatballs.  I wouldn't boil them, as the rolling action could tear them apart. It is more common to poach in a sauce, however water can certainly be used. You will lose some flavor (taste the water afterward, you will see), however, it wouldn't be a reason to avoid the technique if you have a purpose for it.  Lots of things are poached and still have flavor.