Yah. Pretty much you just.. sell the Creatu that has the name, usually. xD
Although, you can also use name tags if you have the name on a particularly valuable Creatu and want to keep the pet but sell the name. You just have to make sure you and your buyer are on the same page about it, and that you keep it all completely private. Otherwise there's a pretty big chance that someone will steal the name; I know Allen lost the name Spy by doing it that way.