I notice he's listed as artist in a few sources, but yeah, I wasn't sure if that also meant box/character illustrations or just in-game art.
I've never heard anyone cite Kojima as doing the art so it took me by surprise. IGA didn't work on the game and she seems to only be employed for his productions.
Either way it's always been a cool drawing style that I wish had been used in more games in the series: kind of anime-esque but highly detailed.