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 ...
they definitely would lose some flavour depending on the time you are going to boil them.
rather just steam them that way you wouldn't loose much of the flavours if you have to go with this method.
What I do is I just sauté them in frying pan for few minutes so they are little browned from outside it enhances their flavour by 10 folds.