Can working out with a stair stepper cause stretch marks.?

Generally NO: This is a vague and generalized question and depends on the patients body habitus. Generally speaking, working out of any kind leads to tightening of muscles and firming and toning. Stretch marks are due to stretch and therefore thinning of the underlying dermis usually due to some kind of weight gain. I.E. Pregnancy.

No: No, but weight gain certainly can -- and does.