Closer confines, having to see the alleged rapist more often, tighter social constraints. I could see an argument for and against.
Yes, there are clearly some different parameters which could either raise or lower the difficulty and trauma associated with it. They're in closer confines which could make it more difficult, they are in a more liberal and educated environment which coudl have less stigma towards rape victims which could make it easier, etc, etc, etc. Vague potential effects of poorly defined parameters aren't a counter to hard numbers outside of the anti-vaccination crowd, however.
If someone can demonstrate what would make a statistically distinct difference in the reporting and why, it would undermine the conclusions of the study. If not, it's safe to assume that the rates of reporting would be similar between the two environments.