A while back when EarthPoker was starting up they had 6 player SNGs for points toward a leaderboard thing and there were 80% bots playing the tables. What you describe is exactly the play they employed and there was NO QUESTION that these were not reall players. This was for play money though, and I have never seen eveidence of this at any site where real money was in play (while it is certainly possible).
That said, that style of play is TOO easy to beat. Just wait till you have the best hand and keep raising. They will gain a lot of chips if noone notices how they are playing because people will continually try to bluff them out not realizing that they have no chance of succeeding.
The question would be was it a PokerFantasy bot or someone's personal bot that they have playing there. In the first case, stop playing the site (or play there more since you are playing against easy targets, your call). Second case, contact support and report the account (OR, buddy list the account and try to find it playing in a cash game....
sucker will wake up in the morning and wonder how Robby the robot got beat so bad)