We’re not botanists, so must stop short of providing a blanket assurance that your ornamental plums are edible. But ornamental fruit trees in general are closely related to the orchard trees grown for their fruit. And while the ornamental plants are grown primarily for their floral display and attractive form, many bear edible fruit.
Among the ornamental plum varieties we have found, the American Plum (prunus americana; wild plum or goose plum) produces fruits that are yellow to red, and are good for making jelly. The fruit of the Mexican Plum (prunus mexicana) is likewise supposed to be especially good for jelly. The Chickasaw Plum (prunus angustifolia) produces edible fruits. Of the two types of Cherry Plum (prunus cerasifera), the Atropurpurea produces edible fruit, while the Thundercloud seldom has any fruit to show for its efforts. If you’re concerned about your plums, a county extension service, college agriculture department, or nearby nursery will be able to give you a definitive answer.