I think it's possible. (although I don't think I would try it with no additional lighting) I would suggest picking a variety that doesn't need as much light and is cold tolerant.

Possible yes but very slow. If he has toms already well along before the cold dark sets in, they might continue producing or at least ripening. Or perhaps he is just giving next year's toms a big head start? Flowering/fruiting plants usually need lots of bright sun light and are likely to be slowed way down without it but if he has a really good greenhouse location that gets the fullest possible amount of light then who knows what could happen.

Thanks for all the advice. What additional sources would you recommend for info on growing tomatoes throughout the winter.