I spoke to an admission rep at Columbia yesterday and she says if the scores are not required, you should only submit them if they can HELP your application. If you did extremely well, then sure, go ahead. If your scores are mid-range or low, however, absolutely do not submit them as it likely can and will be held against you. In cases where the GRE requirement is dropped, your best course of action is to write a killer SOP and have great letters of rec. Best of luck!