vacantlook
Super Moderator
...both definatively state that he was Maiar.
Just because a role playing game says something doesn't make that official in the eyes of the person who created the universe. Tolkien had plenty of room to just flat out say that Bombadil was a maiar, but he didn't. He specifically chose to leave what he was a total undefined thing. So, regardless of what other people who find themselves granted some form of legitimacy after Tolkien's death to grant officiality to anything, that doesn't mean squat when it comes to what Tolkien himself thought.
And to look at it through the lense of the story, we see what the Ring does to TWO maiar in the story itself: both Gandalf and Saruman show how they could easily be taken by the Ring if they were to take possession of it. But Bombadil handles the ring and it has absolutely no pull on him whatsoever. I'd say this points to him not being a maiar, otherwise he'd be affected just the same as Gandalf and Saruman were.