they appear because they were given ratings for the (online) US Chess League a while ago, the ratings being set as their USCF ratings (so that observers knew the USCF rating of any of the players). All the games in the USCL were unrated. And because some of them haven't played any rated games, their ratings are hidden and displayed as Unrated, even though they do have ratings.
I believe players get removed from the list after a year of inactivity (though I'm not sure about this), so they should disappear in about 4 months.
Have you noticed the standard rankings? The first page is filled with tons of players, some are unrated! Can you fix this?
http://www.chess.com/livechess/players?type=Standard&page=1
I won't get to know my real ranking