"Is there any Sway in a Spin in the Standard style of dancing."
Not in the basic version, but yes, it plays an important role in many of the more advanced interpretations being performed to great effect by leading competitors.
"Would a Sway take a couple off balance."
Almost any movement in dance technically takes a couple off balance. The more important question is, would it disrupt their poise, or their SENSE of balance. And the answer to that is NO, not if it is properly coordinated with their movement.