I mean, they mate and make Purple, but, purple was with a normal Reimu . . . Maybe she stole the little one and killed the parents trying to exploit it like a freak or something but shit got bad and tried to get rid of purple before Anon pulled a Big Damn Hero with his foot on her face.
I actually feel it's more under false pretenses. Patchouli would probably reject a half-blind and ugly yukkuri, normally; I'd have loved to find a way to restore her sight, just to see it be violently repulsed by 'her' Reimu.
Burnout, Good Yu's are known to be far more acceptant of those who are different, and since this story implies This Reimu and the Patchouli were good, hard working yet handicapped yu's, they probably won't mind each other's differences.
If they had shown scum aspects you may had a point, but since they didn't and their Kid turned out to be quite nice as well we can say for sure they are good fellas and Patchouli would still accept Reimu regardless if she could see or not.