The answer for this question, as being suggested by other members in this forum, would be both. Atemi is , in fact, both a way to distact and a way to really hit an oponnent. Sometimes it generates a gap in order to perform or change the technique, sometimes it is part or the technique itself. A very important mater is to keep fluidity in every aikistuff, some people incorporate atemi in their techniques stopping them, and that is somethign one must never do.
The sensei of my sensei practiced boxing before aikido and my sensei also practiced an strikelike art such as kempo, both insist in this though they also said that it is not easy to acomplish .
Atemi is sometimes soft, others hard, a kick(!) or a blow, one should practice in order to deal with REAL situation.
BUT PLEASE TAKE CARE OF YOUR UKE!