Re: Is there a list of characters Marvel has the rights to?
Namor isn't split. Universal outright has his rights, inexplicably. He's only very technically a mutant, in a similar but even more distant manner to how Franklin Richards is technically a mutant. He's not, in any way shape or form, an X-character.
( yes, he's appeared as part of the X-Men. . . in terrible comics that, more importantly, long post-date the contracts involved )