I checked into the UMass-Amherst link that you included, and per PA's Dept of Natural Resources, as well, ringnecks are short-ish harmless snakes that simply get into some people's homes & they do not pose a threat. Occasionally they will bite, and some will release a "foul musk."
(That would be enough for me to want to set it free!) But otherwise, no site stated that it *couldn't* be kept...
So, from what I read, seems to be ok to keep it...
However, I also found this: a person in Quebec recorded his progress with having found ringnecks and how the snakes subsequently died from not being able to handle captivity (their scales also seemed to all develop blisters of some sort before death...doesn't sound too pleasant to me...). While your brother probably could keep the snake, it doesn't sound like he should...
Ringneck Diary
Then again, that's all I found in about 5 mins of looking, and I've never heard of the snake before, so I'm certainly no expert. Good luck.