I'm on the prison rotation as a second year in my program. I can't really answer your question about moonlighting/money, though I have seen some good looking offers for post graduate positions in the prison system in many states.
As you probably know, you are treating criminals. Some of whom have raped and murdered other human beings. Others however may have committed other crimes such as fraud or have stolen/committed robbery. I find it interesting to ask some of my patients why they are in jail, most of them answer you truthfully about their circumstances. I find it to be interesting work and I may be cultivating my interest in forensics.
As to your question. YES, you are in increased danger from these individuals. Most of the patients do have an "angle" when they are seeing you voluntarily, even if they have an axis I or II diagnosis. One of the prisoners came to see me (initial visit) to try to get me to help him get out of working in the kitchen. However you do have to realize where you are and who you your patients are. There is some protection such as, when I see patient's in the prison's version of an inpatient psychiatric unit, I am in a room and the prisoner is separated off by enriched glass (hopefully unbreakable), and they are in cuffs.
The guards are also of course there to protect you, though some of the guards are not that much better off than the prisoners. As with any psychiatric facility, watch your back.
