Is this the thing we are talking about?
You may be overestimating the degree of "protection" that you get from the tsuba in these cases. IME (and fwiw, my teacher learned from one of Chiba Sensei's students, and the practice is as Joe describes), if the attack is successful, believe me, you're not saying "whatever" and continuing to "hack away", as you characterize it. You get, um, feedback. The tsuba prevents serious injury; it doesn't mean you never get hit.
It is what I think we are talking about but I am not sure.
Is the point to hit uke's tsuba, and use that to connect and put your weight on them? In which case this is purely an aiki exercise and it's not an application. Or, are you actually trying to hit their wrist?
If you are trying to hit their wrist, then you shouldn't be hitting the tsuba, right?
If you are trying to hit their wrist, are you trying to hurt them during training? What is the point of the feedback you mention? That is feedback that...what happened exactly?