shills... I do know for sure there are "house players" on quite a few poker sites, the poker room pays the house players...
Just to clarify, there are Prop players and there are Shills. Both work for the place they play, but there is a significant difference.
Prop players are paid an hourly wage to start tables, keep games going, etc, but they play with their own money. They keep their winnings and they eat their losses. The only bonus they get is that hours wage. Also, prop players usually have to sit in short handed games or less popular games.
Shills are not only paid an hourly wage, but they also play with house money. There is no financial risk for them. Their goal (in order to keep their job really) is to win money at the games for the house using the houses money.
There is nothing wrong with Prop players at all, however using Shills is immoral at best.