Not sure what an SUA is, but a succenturate lobe usually comes right out w the main placenta. But most midwives check placenta's carefully to make sure a piece is not retained.
I would not recommend pp artificial oxytocin, which would be more likely to trap the extra lobe, than expel it, if it doesn't come out with the main lobe. Of course, if you have recieved artificial oxytocin during labor, that short-circuits your bodies ability to produce it after the birth, and you may benefit from getting it pp if you have gotten it during labor. If the placenta is rushed or pulled, the lobe is more likely to be left behind than if it is left to come naturally.
I do recommend immediate nursing as soon as your baby is breathing, as the best way to facilitate complete placenta expulsion with minimal bleeding.