For Shomenuchi ni (where uke initiates), we use both hands to intecept, so we have to forego that strike. The upper hand tegatanas the shomenuchi and the bottom hand catches the elbow. Then (for kotegaeshi ni) we pivot, bring uke around, reverse direction (another pivot) and strike, then cut the kotegaeshi down/through as we do the final pivot.
If it were Yokomenuchi ni, for instance, we'd intercept with one hand and atemi with the other, then proceed.
Ok, that's the way I was taught but I was watching some clips of Takeno Sensei and it seemed like he was initiating dai ni with shomenuchi. Basically I couldn't tell if it was uke or nage initiating the first movement. That being said, it was an instructional video that was filmed at very slow, film-study, speed.