Personally I see no problem with it so long as it's at least reasonably explained in some way (inherited the name through marriage, adopted, etc.). While mechanically speaking there's no issue, it's just the kind of thing that's good to have an explanation for during RP moments.
In this case it's also the kind of thing a DM can handwave aside (ex. just declare that the Clements are a rare elven noble house, and swap the one mentioned Clement to be an Elf if they show up). At least in the case of the Clements this isn't too difficult (unlike say Vernissant or Stavian, for example). This is the sort of thing that depends heavily on the DM's willingness to go along with the player's intentions over the established structure. I for example would have no problem bending plot elements to better fit my players' intentions, though I know other DMs would be much more strict about that sort of thing.