I certainly believe that sutemi techniques are aikido, and like all techniques, they are worthwhile to practice. They are a good lesson in timing, ma ai and really good for learning to relax your body. I often teach them in class, and I use them in randori too, but, like all techniques, it depends on the my interaction with my uke's as to which sutemi waza I do. In randori for example, regardless of the number of uke's, I try not to do sutemi going backwards, I will always aim for waza where I can bowl uke over with my body, which in turn bowls other uke's over with uke (I hope that's come out right). The placement of uke's when doing is important though as you don't want to be on the floor with an uke standing over you, unless your really really good at hanmi handachi waza of course
As for Boon's last statement about atemi being indespensible when facing multiple opponents, absolutely right, whether multiple or single.