It's not just an obscenity filter. The pet naming rules are the regular naming rules, and they don't allow you to include a title as part of a name. So you can't have a mister or a miss, a princess or a king, a general or a captain, etc. I guess they didn't want people pretending to have PvP titles they didn't earn, and such, when they originally wrote the name rules. This is pretty silly for pets, though, since a lot of popular pet names are titles, like Lady and Duke.
Why does sewage flow uphill leaving Undercity?