And, barring injury or infirmity, all greyhounds can and will sit. They won't sit, however, if you talk the both of you into believing they can't/won't.
Yup, they can sit and/or learn anything other dogs can. 7 of our 8 greyhounds sat or sit on command. Dancer had us trained that when we said "Dancer SIT." She would look at us with her big lipid brown eyes and a forlorn look on her face and we would give her a treat. :lol