I've been thinking about this, and I do think that even if a facility did a background check, the aides would likely not be informed of the findings.
Because of current privacy laws, it seems like information like this would be given on a "need to know" basis and who knows what they consider necessary?
What got me thinking about this is a new resident we got at work a couple of weeks ago.
Now, my facility is for the developmentally disabled, mostly children and young adults, so we don't have many cases where you worry about that sort of thing.
We do have one resident who was "normal" until he got in a motorcycle accident when he was a fugitive running from the cops, but his crime was not a violent one, it was some kind of theft.
However, we got a new resident a couple of weeks ago and were not told anything about him other than the basics - down's syndrome, able to walk and talk, and sometimes resists care.
One of the nurses I work with was going back in his chart to find some information she needed on one of his meds or treatments, and found some disturbing information. At a group home he lived in previously, he was often found stabbing objects with knives, had physically harmed other residents in the group home, and on a car ride, had attempted to open the door of the car. We were not informed of ANY of this. Whether our management was informed of these issues or not, I don't know, but the nurses and aides were not.
Now, privacy or not, this seems like the sort of information caretakers should know, since there are 80 other kids in the facility, and most are not able to walk or defend themselves in any way. He is in a room with 3 other boys, and has a history of violence with fellow residents. It seems dangerous and irresponsible to me, that we are not informed of issues like this.