Dear OP,
Since updates are submitted and confirmed online, I wouldn't expect Tufts to ever get back to you about it.
That still doesn't really answer the question of receptivity. I think at worst, it annoys them to have another paper to staple to your file and at best it is reviewed by the committee. I figure I have nothing to lose from updating them, so I sent them one 6 weeks ago and I am sending another one today because I have significant updates for them. In both cases, the updates were regarding something that would add a line to my resume (a useful rule of thumb that I picked up from some SDN thread a while back), if I were to update the my resume from when I sent in my primary in June. I think if your update was significant, then you did the right thing and that you shouldn't worry about not hearing back from them.
It also says on the portal, "You are welcome to upload memos from yourself to our admissions committee."