Can they retrieve eggs from a person without a cervix who has had a hysterectomy?

Yes. Yes. It's simple. An egg retrieval involves placing a needle into the ovary. No cervix or uterus needed.
Usually. After hysterectomy-including-cervix (total hysterectomy, ) a woman may be suitable for ultrasound-guided egg retrieval just like any other if the ovaries remain. In some cases after major pelvic surgery transvaginal egg retrieval could be difficult or impossible if the pelvic anatomy has been significantly distorted.