What archetypal character does Tom Simson represent?

Tom is known at "the innocent" of Sandy Bar, but really the archetype that best fits him is "the child," because he is endlessly optimistic, hopelessly naive, loyal to a fault, and mainly concerned with happiness. We know few basic things about Tom: he is terrible at poker; he has run off with his girl friend, Piney Woods, to get married in Poker Flats, against the wishes of her father; and he is loyal to the gambler Oakhurst, who did him a good turn by winning all of Tom's money, then taking him aside and telling him never to gamble again and giving the money back.
In fact, it is Tom's optimism that gets the travelers in trouble, since he insists they stay the night in the cabin even with bad weather threatening. Even after they are snowed in, Tom continues to see the bright side, saying that they will be snug in the cabin "for a week" until the snow melts. In fact, the purity of Tom and Piney softens or inspires the other travelers. Even Mother Shipton sacrifices her food (and life) for the sake of the "kids."

Tom Simson represents the character archetype known as "The Innocent." In fact, that's exactly how he's referred to in the story itself. And Tom certainly displays all the character traits associated with this archetype. He's wholesome, a little naive perhaps, but bursting with optimism. He's a genuine all-round nice guy, always keen to please and keener still to help others in need. We see this towards the end of the story when he ventures out into the snow to get help for Oakhurst and the other stranded travelers. 
A downside of the "Innocent" archetype is that they are easily led, too trusting. For instance, in the case of Tom, he remains in awe of Oakhurst despite the fact that he once lost a lot of money to him at the poker table. The boundless optimism of the "innocents" blinds them to their own weaknesses, making it easier for them to be exploited and manipulated by others. These are certainly not the characteristics of someone hoping to make money at poker. No wonder Oakhurst advises Tom never to play the game again.