Will a purple leaf plum (ornamental) cross pollinate a fruit bearing European plum tree?
The purple leaf ornamentals are diploid plums and they often cross with the Japanese types which are also diploids but Euros are hexaploid or some other higher ploidy and will not generally cross. On the other hand many Euros are self-pollinating, look up your variety and make sure it needs a pollinator.
Have you tried grafting Euros and Japanese onto the same tree?? I think I've someone had success doing it...