I believe the decision to enter a name into the "raffle" more times in exchange for additional tesserae is morally correct; however, I believe the system that created such a process is morally suspect.
Katniss explains to readers in chapter one how the tesserae process works.
Say you are poor and starving as we were. You can opt to add your name more times in exchange for tesserae. Each tessera is worth a meager year's supply of grain and oil for one person. You may do this for each of your family members as well. So, at the age of twelve, I had my name entered four times. Once, because I had to, and three times for tesserae for grain and oil for myself, Prim, and my mother.
In other words, if you want more food for your family, you have to apply for the reaping more times. It's a straightforward risk vs. reward decision. I don't see that as being morally wrong, especially when it is done for survival. Katniss can get a lot more food and oil for her family, but her risk of being chosen for the Hunger Games is now higher.
I do think the entire system is corrupt, though. Katniss is operating within the rules of the system for the welfare of her family, but the system is lopsided. It practically guarantees children from poor families will always be selected in the reaping. Poor families need the tesserae; therefore, a person from a poor family is more likely to have his or her name in the reaping selection more times than a person from a wealthy family. This means a person from a poor family is statistically more likely to be selected for The Hunger Games. I think inherently unfair systems like that are morally corrupt.