...Well, you know, people who don't want him say 3rd and people who want him mostly say 1rst, but in any case,
SAKURAI HIMSELF said that he sees him as 1rst party so even if he has had to go through all the third-party-asking-to-use-the-character thing,
which I'll afterwrads say why I greatly doubt it, he won't take a third party place.
Also, when you do a little research.... you don't find out everything you need to come to a flawless conclusion, but if you like geno and want him in, you'll like this answer.
Mario RPG was NOT MADE by Square.
Mario RPG, its characters, story and music should normally all belong to nintendo.
Remember how the Square Logo was shown after the nintendo one when you turn on your SNES? not only that, but square's logo isn't even on the game's box or label.
And here's why.
Square made the GAMEPLAY of mario rpg. They made the game with squaresoft because they were and still are the best RPG making company ever, and they wanted the game to be a great one.
As far as I know, only the combat, map, levelling, character switching and stats, item effects and ETC (INSERT OTHER GAMEPLAY ASPECTS ) is Square.
Square is Credited at the end of SuperStar Saga for Geno's cameo appearance, hinting at the fact that they indeed have part of the rights on him.
If it was a nintendo or square person that created Geno, who the hell knows,
but for some reason they have some rights on him. But in any case, Mario RPG is a Nintendo Game with Final Fantasy References, not the other way around, so the Game has a Nintendo SOUL to it (loll).
Enough extreme fanboyism for today, me thinks.