I would never consider creating a character directly related to a canon outside of fanfiction, but my first character Ponessa (Who was recently seen at the DH memorial) is/was distantly related to Snape. I've seen a lot of people want to be descendants of snape, but fail to see that just because you are related to someone does NOT mean you are just like them. Even so, Ponessa was SO distantly related, she didn't even recall what side of the family he had been on.

I don't find there's MUCH harm in being related, but if someone is claiming to be the daughter/son of a canon character, I, myself, will ignore them completely. I DON'T even know how to deal with that.