If you ovulate later than the normal 14 days after lmp, would the dating ultrasound this and would it affect your due date?

Yes: Estimated due dates are just that - estimates. 1st trimester dating ultrasounds are based entirely on size measurements, regardless of lmp/ovulattion. One measurement is the "crown rump length" and another is the average size of the gestational sac. If you conceived later, your ultrasound should measure smaller than the expected dates based on LMP and your due date would be later.